A 

0 
0 
1 

0 
9 
5 

3 
9 
8 

2 

_^_ ^ 

FERTILIZER  EXPERIMENTS  WITH 


CITRUS  TREES. 


JL^-ailla 


y.,    OfyrtJ 


THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


PNIVEB8ITY  OJF  CALIFORNIA  PPBLICATIOW8 

COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


t 


FERTILIZER  EXPERIMENTS  WITH 
CITRUS  TREES 


BY 
R.  S.  VAILE 


BULLETIN  No.  345 

Junk,  1922 


UNIVERSITY  OF  CALIFORNIA  PRESS 

BERKELEY 

1922 


David  P.  Barrows,  President  of  the  University. 

EXPERIMENT  STATION  STAFF 

HEADS  OF  DIVISIONS 

Thomas  Forsyth  Hunt,  Dean. 

Edward  J.  Wickson,  Horticulture  (Emeritus). 

,  Director  of  Resident  Instruction. 

Clarence  M.  Haring,  Veterinary  Science,  Director  Agricultural  Experiment 
Station. 

B.  H.  Crocheron,  Director  of  Agricultural  Extension. 

H.  J.  Webber,  Citriculture,  Director  Citrus  Experiment  Station. 

C.  B.  Hutchison,  Plant  Breeding;  Director  of  the  Branch  of  the  College  of  Agri- 

culture at  Davis. 
H.  E.  Van  Norman,  Dairy  Management. 
William  A.  Setchell,  Botany. 
Mver  E.  Jaffa,  Nutrition. 
Ralph  E.  Smith,  Plant  Pathology. 
John  W.  Gilmorx,  Agronomy. 
Charles  F.  Shaw,  Soil  Technology. 
John  W.  Gregg,  Landscape  Gardening  and  Floriculture. 
Frederic  T.  Bioletti,  Viticulture  and  Fruit  Products. 
Warren  T.  Clarke,  Agricultural  Extension. 
Ernest  B.  Babcock,  Genetics. 
Gordon  H.  True,  Animal  Husbandry. 
Walter  Mulford,  Forestry. 
James  T.  Barrett,  Plant  Pathology. 
Fritz  W.  Woll,  Animal  Nutrition. 
W.  P.  Kelley,  Agricultural  Chemistry. 
H.  J.  Quayle,  Entomology. 
Elwood  Mead,  Rural  Institutions. 
H.  S.  Rexd,  Plant  Physiology. 
L.  D.  Batohxlor,  Orchard  Management. 
J.  C.  Whitten,  Pomology. 
•Frank  Adams,  Irrigation  Investigations. 

C.  L.  Roadhouse,  Dairy  Industry. 
R.  L.  Adams,  Farm  Management. 

W.  B.  Herms,  Entomology  and  Parasitology. 

F.  L.  Griffin,  Agricultural  Education. 
John  E.  Dougherty,  Poultry  Husbandry. 

D.  R  Ho agl and,  Plant  Nutrition. 

G.  H.  Hart,  Veterinary  Science. 

L.  J.  Fletcher,  Agricultural  Engineering. 
Edwin  C.  Voorhies,  Assistant  to  the  Dean. 

citrus  experiment  station 

division  of  orchard  management 

L.  D.  Batchelor  R  S.  Vaile 

G.   J.    SURR 


*  In  coSperation  with  Division  of  Agricultural  Engineering,  Bureau  of  Public  Road*.  U.  S. 
Department  of  Agriculture. 


FERTILIZER  EXPERIMENTS  WITH 
CITRUS  TREES1 

By  E.  S.  VAILE 


CONTENTS 

PAGE 

Foreword 465 

Locations 466 

Introduction  and  Review  of  Literature 467 

Limitations  of  Orchard  Field  Trials 472 

Rubidoux  Experiments ,. 473 

Outline  Plan  of  Experiments 473 

Planting  the  Orchard 473 

Care  of  the  Orchard 475 

Irrigation 476 

Differential  Treatments *. 476 

Yields 479 

Additional  Data 482 

Mottle  Leaf 484 

Discussion 486 

Arlington  Heights  Experiment 488 

Plan  of  the  Experiments 488 

Yields 494 

Mottle  Leaf , 496 

Discussion 498 

Chaffey  Experiment 502 

Plan  of  the  Experiments 502 

Discussion 503 

Additional  Growers'  Trials 506 

California  Citrus  Soils 508 

Conclusions  511 


FOREWORD 

The  fertilizer  experiments  herein  described  are  the  results  of  five 
separate  field  trials  located  in  four  different  citrus  growing  centers. 
The  experiments  were  planned  and  executed  by  various  members  of 
the  Citrus  Experiment  Station  staff  and  the  respective  owners  of  three 
of  the  properties. 


Paper  No.  83,  University  of  California  Graduate  School  of  Tropical  Agricul- 
ture and  Citrus  Experiment  Station,  Riverside,  California. 


210358 


466  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

Special  credit  should  be  given  Ralph  E.  Smith  and  his  co-workers, 
J.  W.  Mills  and  T.  Francis  Hunt,  for  the  planning  and  the  early 
operation  of  the  Rubidoux  trial.  During  the  subsequent  progress  of 
this  trial  J.  H.  Norton,  J.  Eliot  Coit,  H.  J.  Webber,  and  W.  M.  Mertz 
were  largely  responsible  for  its  success. 

The  Arlington  trial  was  planned  and  put  into  effect  by  H.  J. 
Webber,  W.  P.  Kelley,  and  W.  M.  Mertz.  Special  credit  for  the  suc- 
cess of  this  trial  is  also  due  to  the  careful  supervision  of  the  field  work 
by  Gordon  Surr. 

The  Ontario,  Chula  Vista,  and  Naranjo  trials  were  planned  by 
R.  S.  Vaile  and  his  co-workers  and  carried  into  effect  by  the  respective 
property  owners.  Charles  J.  Booth's  cooperation  in  the  Ontario 
experiments  and  J.  A.  Prizer's  attention  to  the  Chula  Vista  trials  were 
in  a  great  measure  responsible  for  their  success. 

For  the  past  two  years  R.  S.  Vaile  has  been  in  charge  of  the  first 
tw"o  mentioned  experiments  and  has  been  associated  with  the  other 
trials  from  their  beginning. 

(Signed)   L.  D.  Batchelor, 
In  charge,  Orchard  Management  Division,  Riverside. 

Experiments  on  the  fertilization  of  citrus  fruit  trees  are  here 
reported.  Navel  and  Valencia  oranges,  Eureka  and  Lisbon  lemons, 
are  included  in  the  report. 

This  is  intended  as  a  progress  report  covering  the  years  1907- 
1920  inclusive. 


LOCATIONS 
RUBIDOUX 

The  experiment  of  longest  standing  is  located  on  the  University 
of  California  Citrus  Experiment  Station's  property,  Rubidoux  site, 
Riverside.  The  soil  is  partly  Sierra  loam  and  partly  Placentia  loam. 
The  trees  were  planted  in  1907.  Differential  fertilizer  treatments 
were  installed  at  once  and  have  been  continued  to  date  without 
interruption.  All  four  varieties  of  citrus  trees  mentioned  above  are 
included  in  the  experiment. 

ARLINGTON 

A  second  trial  is  located  in  an  old  Navel  orange  grove  in  Arlington, 
planted  in  1890  on  Placentia  loam  soil.  The  trials  were  conducted 
from  April,  1915,  to  February,  1920,  inclusive. 

- 

••       • 

J  >    .   I  < 


BULLETIN   345]  FERTILIZER  EXPERIMENTS   WITH   CITRUS  TREES  467 


ONTARIO 


A  third  trial  is  located  on  an  old  Navel  orange  grove  at  Ontario, 
planted  on  Hanford  gravelly  loam  in  1899.  The  trials  were  conducted 
from  September,  1915,  to  February,  1921,  inclusive. 


CHULA  VISTA 

A  fourth  trial  is  located  on  a  young  Eureka  lemon  grove  at  Chula 
Vista,  planted  in  1915  on  Kimball  sandy  soil.  The  trial  was  con- 
ducted from  June,  1915,  to  December,  1920. 

NARANJO 

A  fifth  trial  is  located  on  a  Navel  grove  at  Naranjo,  planted  in 
1907  on  San  Joaquin  loam  soil.  The  trial  was  conducted  from  March, 
1916,  to  December,  1920,  inclusive. 

Reference  is  also  made  to  several  other  growers'  field  trials  with 
fertilizers,  and  to  orchard  practice  surveys. 


INTRODUCTION  AND  REVIEW  OF  LITERATURE 

The  conclusion  that  citrus  groves  in  southern  California  must  be 
fertilized  if  they  are  to  be  profitable  is  supported  by  surveys  made  by 
Experiment  Station  workers  during  the  past  fifteen  years  and  by 
abundant  field  evidence  that  is  recognized  as  valid  by  all  successful 
growers. 

On  the  other  hand,  there  is  little  definite  information  concerning 
either  the  specific  kinds  and  amounts  of  fertilizer  or  the  time  and 
method  of  application,  from  which  the  greatest  returns  may  be 
expected. 

The  general  field  practice  of  successful  growers  might  be  expected 
to  give  valuable  information  on  these  points,  but  there  has  been  so 
much  variation  in  the  use  of  fertilizers  and  in  cultural  practice  that 
it  is  very  difficult  to  determine  what  particular  operation  is  respon- 
sible for  success  or  failure. 

A  field  survey  conducted  during  1907  by  Smith,  Ramsey,  and 
Babcock2  records  the  fertilizer  treatment  for  at  least  a  five-year  period 
on  each  of  50  groves.  These  groves  were  scattered  throughout  the 
citrus  districts  and  in  each  case  were  well  above  the  average  in  yield 
for  their  locality.  On  an  average,  90  pounds  of  actual  nitrogen  was 
applied  per  acre  annually.     The  range  of  application  was  from  21 

2  Unpublished  notes,  Citrus  Experiment  Station,  1907. 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 

oeouci  CV     PA1  imRNlA 


468 


UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION 


pounds  nitrogen  annually  to  295  pounds  annually  for  the  five-year 
average.  No  striking  differences  in  crop  yields  or  quality  were  shown 
from  this  wide  range  in  the  use  of  nitrogen. 

In  1915  a  partial  survey  of  the  Ontario-Upland  colony  was  under- 
taken. The  accompanying  graph  (fig.  1)  shows  the  yields,  together 
with  the  amount  of  nitrogen  actually  applied  annually  on  ten  groves 
for  which  at  least  five  years'  records  were  available. 


Yield;-  field 
boxes  per  acre 


Nitrogen 
pounds  applied 
per  acre 


( 


-) 


8oo 

Uoo 

700 

r,oo 

^00 

=100 

» 

/ 
/ 

1(00 

\ 
\ 

t 
/ 

\ 
\ 

200 

JQQ 

*- 

> 

* 

\ 

\ 

\ 

200 

\ 

\ 

k. 
\ 

\ 

inn 

inn 

V 
X 

/ 
* 

\ 

n 

n 

Grove  Hot 


8 


10 


Fig.  1. — Graph  showing  relation  of  yield  to  quantity  of  nitrogen  applied. 
Average  annual  yield  for  five  years  (solid  line)  and  average  annual  application 
of  nitrogen  (broken  line)  on  ten  groves  in  Ontario-Upland  colony. 

The  heavily  fertilized  groves  show  a  marked  tendency  to  be  heavy 
producers.  Again,  however,  there  is  no  definite  evidence  for  choice 
between  fertilizer  materials. 

During  1919-1920  a  similar  survey  was  conducted  in  the  San 
Dimas-Covina  district.  Fifty  groves  were  listed,  for  which  five-year 
records  were  available.  Of  these  fifty  groves,  the  nine  with  the  largest 
nitrogen  applications  (i.e.,  176  to  275  pounds  per  acre  annually) 
produced  an  average  of  240  field  boxes  of  fruit  per  acre.  The  nine 
groves  with  the  smallest  nitrogen  applications  (i.e.,  76  to  100  pounds 
per  acre  annually)  yielded  255  field  boxes  per  acre  annually,  indi- 
cating that  in  these  groves  the  smaller  application  of  nitrogen  had 
maintained  the  yields  as  well  as  the  larger  applications  had.  Other 
factors  may  have  existed,  but  the  yields  were  reasonably  good  with 
either  amount. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  469 

Fertilizer  field  trials  with  citrus  trees  have  been  reported  from 
Florida,  Cuba,  Porto  Rico,  Spain,  Italy,  and  elsewhere.  The  results  of 
such  trials  are  of  only  passing  interest  to  California  growers  because 
of  the  wide  differences  of  environment.  It  may  be  instructive  to 
note,  however,  that  the  Porto  Rico  trials3  showed  the  greatest  increase 
in  yield  following  the  use  of  a  complete  fertilizer,  and  that  the  addi- 
tion of  nitrogen  was  more  effective  than  the  addition  of  any  other  of 
the  simple  elements. 

The  amount  of  fertilizer  commonly  used  a  few  years  ago  on  the 
orange  groves  of  Spain,  when  reduced  to  essential  plant  foods  per 
acre,  has  been  stated  to  be  as  f ollows  :4 

Nitrogen  from  75  to  90  pounds  per  acre. 

Phosphoric  acid  (P205)  from  75  to  90  pounds  per  acre. 

Potash  (K20)  from  30  to  60  pounds  per  acre. 

A  surprisingly  large  proportion  of  the  quantity  of  material  that 
has  been  published  in  California  on  the  general  question  of  citrus 
fertilization  is  but  a  reflection  of  opinion  or  casual  observation  rather 
than  the  report  of  experiments. 

Briggs,  Jensen,  and  McLane5  in  1916  published  the  results  of  a 
careful  field  survey  covering  130  orange  groves  and  45  lemon  groves 
in  Riverside  and  San  Bernardino  counties.  They  stated  that ' '  orchards 
fertilized  with  organic  substances,  such  as  stable  manure  or  cover 
crops  plowed  under,  usually  show:  d  less  mottling  than  groves  supplied 
principally  with  commercial  fertilizers.  Groves  which  for  some  years 
had  received  only  the  'complete'  fertilizers,  in  general  use  in  the 
areas  studied,  were  badly  mottled  in  all  cases,  so  far  as  observed  in 
these  studies.  This  was  also  the  case  where  sodium  nitrate  was  used 
alone  or  as  the  principal  fertilizer  for  some  years.  An  impartial 
statistical  study  of  the  data  from  individual  orange  groves  shows  that 
approximately  one-half  the  mottling  can  be  accounted  for  by  the  low 
humus  content  of  the  soil. ' ' 

The  same  authors6  in  discussing  the  mulched-basin  system  of 
irrigated  citrus  culture  submit  that  a  marked  improvement  followed 
the  installation  of  this  system  on  certain  test  plots  under  their  direc- 


8  C.  F.  Kingman,  Citrus  fertilization  in  Porto  Eico.     Porto  Eico   Agr.   Exp. 
Sta.,  Bull.  18,  p.  33,  1915. 

4  De  Mendoza,  Fertilizing  oranges  in  Spain,  Calif.  Cultivator,  vol.  41,  p.  559. 

5  L.  J.  Briggs,  C.  A.  Jensen,  J.  W.  McLane,  Mottle  leaf  of  citrus  trees,  Jour. 
Agr.  Eesearch,  vol.  6,  no.  19,  pp.  721-739,  1916. 

s  The  mulched-basin  system  of  irrigated  citrus  culture  and  its  bearing  on  the 
control  of  mottle  leaf,  U.  S.  D.  A.,  Bull.  499,  31  pp.,  February,  1917. 


470  l "NIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

tion.  The  improvement  was  evidenced  by  the  increased  vigor  and 
yield  of  the  trees,  the  disappearance  of  mottle-leaf,  the  elimination 
of  soil  plow-sole,  and  the  increase  of  humus. 

McBeth7  in  discussing  the  relation  of  soil  nitrogen  to  the  nutrition 
of  citrus  plants,  states  that  "the  furrow  system  of  irrigation  fre- 
quently causes  a  very  unsatisfactory  distribution  of  soil  nitrates.  In 
many  citrus  groves  more  than  two-thirds  of  the  nitric  nitrogen  in 
the  upper  four  feet  of  soil  is  found  in  the  surface  six  inches,  in  which, 
because  of  frequent  cultivation,  few  feeding  roots  are  found,"  and 
"where  the  furrow  system  of  irrigation  is  employed,  the  fertilizing 
materials  should  be  plowed  down  somewhat  deeper  than  the  land  is 
cultivated."  A  large  part  of  the  work  reported  on  by  McBeth  was 
done  on  the  soils  of  the  fertilizer  plots  of  the  University  of  California 
at  the  Rubidoux  site,  Citrus  Experiment  Station,  Riverside. 

Young8  published  an  article  on  the  effect  of  fertilizer  on  the  com- 
position and  quality  of  oranges,  based  on  the  results  of  field  trial  by 
the  Citrus  Experiment  Station  (other  phases  of  these  trials  will  be 
discussed  in  the  present  publication).  In  reviewing  previous  work  on 
the  subject,  he  shows  that  most  of  it  has  been  unsatisfactory  because  it 
was  based  too  largely  on  observations  of  trees  where  the  feeding  con- 
ditions were  not  completely  controlled.  Young  states  in  conclusion 
"that  nitrogen  is  the  only  fertilizer  which  in  this  experiment  served 
to  exercise  a  specific  effect  on  the  composition  of  oranges.  Applica- 
tion of  nitrogen  to  the  soil  resulted  in  a  slightly  lower  amount  of 
sugar,  a  somewhat  coarser  fruit,  and  a  little  less  juice  in  the  orange. ' ' 
These  modifications  in  quality,  however,  were  in  no  case  sufficient  to 
lower  the  commercial  grade  of  the  fruit. 

Webber9  has  twice  presented  brief  progress  reports  on  the  field 
trials  of  the  University  of  California  at  the  Rubidoux  site,  Citrus 
Experiment  Station,  Riverside.  These  reports  emphasize  particularly 
three  points: 

1.  Unfertilized  trees,  under  the  conditions  of  the  experiment,  were 
not  producing  satisfactory  crops  of  fruit  at  six  and  seven  years  of  age. 


i  McBeth,  I.  J.,  Relation  of  the  transformation  and  distribution  of  soil  nitro- 
gen to  the  nutrition  of  citrus  plants,  Jour.  AgT.  Research,  vol.  9,  no.  7,  pp.  183- 
252,  May,  1917. 

*  Young,  H.  D.,  Effect  of  fertilizers  on  the  composition  and  quality  of  oranges, 
Jour.  Agr.  Research,  vol.  8,  no.  4,  pp.  127-138,  January,  1917. 

•  Webber,  H.  J.,  Fertilizer  experiments  with  citrus  fruits,  Calif.  Cultivator, 
vol.  41,  p.  596,  December  11,  1913;  The  fertilizer  requirements  of  citrus  trees, 
Proceedings  of  45th  Fruit  Growers'  Convention  at  Los  Angeles,  Nov.  10-14,  1914, 
p.  101,  also  in  Monthly  Bulletin,  Calif.  State  Com.  Hort.,  vol.  IV,  p.  225,  June, 
1915. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  471 

2.  Nitrogen  was  the  only  plant  food  element  that  measurably 
increased  crop  production  at  these  ages. 

3.  Mottle  leaf  had  developed  by  the  sixth  year  to  a  rather  alarming 
extent  on  four  out  of  five  plots  receiving  applications  of  nitrate  of 
soda,  but  not  so  noticeably  on  plots  receiving  nitrogen  from  dried 
blood  or  stable  manure. 

Vaile10  gave  a  progress  report  on  the  Arlington  Grove  experiment 
before  the  June,  1920,  meeting  of  the  California  Citrus  Institute, 
emphasizing : 

1.  Commercial  fertilizer  with  a  high  percentage  of  nitrogen  stim- 
ulated the  trees  to  set  a  good  crop  of  fruit  the  same  spring  the  fertilizer 
was  applied,  but  trees  so  fertilized  did  not  recover  from  mottle  leaf  so 
well  as  might  be  desired. 

2.  The  mulched-basin  system  of  culture  had  a  markedly  beneficial 
effect  temporarily,  as  measured  both  by  crops  and  by  general  tree 
vigor;  but  at  the  end  of  five  years  this  had  yielded  to  evidence  of 
injury  both  in  crop  and  tree  appearance  from  mottling. 

3.  Stable  manure  used  consistently  for  five  years  left  the  trees  in 
far  better  condition  than  after  any  other  type  of  treatment,  although 
the  beneficial  response  was  neither  so  rapid  nor  so  pronounced  as  that 
which  followed  the  two  treatments  mentioned  above. 

Mertz11  has  reported  the  results  in  certain  of  the  University  of 
California  plots  at  the  Kubidoux  site,  Citrus  Experiment  Station, 
Riverside,  which  indicate  a  striking  increase  in  citrus  yields  due  to 
green  manuring. 


io  Vaile,  R.  S.,  Progress  Report  on  Arlington  Grove  Experiment,  California 
Citrograph,  vol.  6,  p.  44.     December,  1920. 

n  Mertz,  W.  M.,  The  use  of  green  manure  crops  in  southern  California.  Univ. 
Calif.,  Agr.  Exp.  Sta.,  Bull.  292,  1918. 


472  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


LIMITATIONS  OF  ORCHARD  FIELD  TRIALS 

Batchelor  and  Rood12  have  pointed  out  the  great  effect  which 
inherent  variation  of  trees  and  soil  has  on  the  accuracy  of  field  trials 
with  fruit  trees.  They  conclude  that  four  repetitions  of  each  treat- 
ment should  be  used,  and  that  such  repetitions  should  be  mathe- 
matically distributed  throughout  the  experimental  area.  The  majority 
of  orchard  field  trials  have  not  been  arranged  to  satisfy  these  require- 
ments; in  faet,  the  limitations  of  space  and  expense  will  always  make 
it  difficult  to  do  so.  Particularly  is  this  true  when  it  is  desired  that 
the  field  trial  shall  answer  in  detail  many  questions  concerning  the 
exact  type  of  fertilizing  material  to  use,  the  economic  quantity,  and 
the  most  advantageous  time  and  method  of  application.  Then,  too, 
it  is  frequently  true  that  in  a  series  of  fertilizer  treatments  some  cul- 
tural operations  should  he  modified  in  order  to  give  the  optimum 
results  from  the  particular  fertilizer  applied.  It  becomes  exceedingly 
difficult,  therefore,  to  determine  to  what  extent  any  change  in  yield 
has  been  caused  by  the  fertilizer,  or  by  change  in  cultural  treatment. 

The  writer  believes  that  it  is  often  best  to  limit  field  trials  with 
orchard  crops  to  comparative  tests  of  complete  systems  of  manage- 
ment, without  attempting  too  close  an  analysis  of  all  the  individual 
factors  that  may  be  involved.  At  best  it  is  obviously  impossible  to 
work  with  all  soil  types,  or  with  large  numbers  of  individual  trees. 
Practical  deductions  must  therefore  be  drawn  cautiously  and  with 
due  allowance  for  changing  environment. 

The  orchard  trials  that  form  the  basis  for  this  report  are  all  subject 
to  certain  of  the  limitations  just  mentioned.  There  is  lack  of  a 
sufficient  number  of  mathematically  distributed  repetitions  to  offset 
the  variability  in  soil  that  is  apparent;  at  times  cultural  operations 
have  been  kept  too  empirically  rigid,  as  among  the  different  plots, 
for  the  best  practical  results;  frequently  the  attempt  has  been  made 
to  draw  fine  distinctions  between  fertilizer  treatments  that  were 
actually  too  essentially  similar  for  contrast.  But  despite  these  short- 
comings there  are  many  indications  that  seem  indisputable  and  that 
have  real  significance  in  any  orchard  management  program.  In  this 
report  a  distinct  effort  has  been  made  to  combine  the  results  of  closely 
similar  treatments  in  order  to  strengthen  the  probability  of  correct 
deductions. 

The  details  of  each  of  the  orchard  trials  will  be  treated  separately, 
with  a  genera]  resume  at  the  close  of  the  report. 

'-  Batchelor,  L.  I)..  nn<l  Reerl,  IT.  8.,  Relation  of  the  variability  of  yields  of 
fruit  trees  to  the  accuracy  of  field  trials,  Jour,  of  Agr.  Res.,  vol.  12,  p.  245,  Febru- 
ary  4^U8. 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  473 

I.     RUBIDOUX  EXPERIMENTS 

OUTLINE   PLAN   OF   EXPERIMENTS 

When  the  University  of  California,  Citrus  Experiment  Station  was 
established  at  Riverside,  one  of  the  first  experiments  undertaken  was 
a  test  of  the  effect  of  various  fertilizers  on  oranges  and  lemons.  These 
field  trials  were  laid  out  and  planted  in  April,  1907.  In  the  original 
plan  of  the  experiment  there  are  20  plots  lettered  from  A  to  T 
inclusive,  each  one  of  which  is  3  trees  wide  by  8  trees  long  and  is 
surrounded  on  all  sides  by  a  guard  row.  Each  plot  contains  6  Wash- 
ington Navel  orange  trees,  6  Valencia  orange  trees,  6  Eureka  lemon 
trees,  and  6  Lisbon  lemon  trees,  all  of  which  are  budded  on  sweet 
orange  root  stocks.  The  trees  are  planted  20  feet  apart  in  squares, 
giving  108  trees  to  the  acre.  At  the  same  time,  a  second  series  of 
trees13  was  planted  to  test  the  effect  of  different  root  stocks,  including 
sweet  orange,  on  citrus  varieties.  These  trials  have  received  different 
fertilizer  and  cultural  treatment  from  that  of  any  of  the  20  fertilizer 
plots  A  to  T.  And  as  it  has  been  thought  interesting  and  entirely 
fair  to  compare  the  trees  on  sweet  orange  root  with  those  in  the  ferti- 
lizer experiment,  plots  U  and  V  are  included  in  the  present  summary. 
Lisbon  lemons  are  not  represented  in  these  plots.  The  trees  in  the 
plot  growing  on  hardpan  land,  enumerated  by  Bonns  and  Mertz,  have 
not  been  included  in  this  report.  The  accompanying  diagram  (fig.  2) 
shows  the  arrangement  of  all  the  trees  and  plots. 

PLANTING    THE    ORCHARD 

A  considerable  portion  of  the  land  utilized  for  these  field  trials 
had  been  under  cultivation  before  the  planting  of  the  present  orchard. 
At  the  time  the  University  leased  the  property  the  part  occupied  by 
plot  U  was  entirely  virgin  soil,  never  having  been  cleared  of  its  native 
vegetation.  Plots  A,  B,  C,  D,  E,  F,  G,  H,  and  the  western  part  of 
plots  I,  J,  K,  L,  were  above  the  old  irrigation  ditch.  This  land  had 
been  dry-farmed  to  barley,  wheat,  and  kafir  corn  for  nine  years.  By 
1905  and  1906  the  barley  crops  had  become  very  poor.  Below  the  old 
ditch  which  ran  diagonally  through  the  plots  K,  L,  M,  I,  and  J,  the 
land  had  been  irrigated  and  cropped  to  melons  two  years;  sweet 

13  For  a  full  description  and  discussion  of  these  trials  see  Bonns,  W.  W.,  and 
Mertz,  W.  M.,  Experiments  with  stocks  for  Citrus,  Calif.  Agr.  Exp.  Sta.,  Bull.  267, 
1916. 


474 


INIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


potatoes,  two  years,  Irish  potatoes,  two  years,  and  tomatoes,  one 
year.  Near  the  center  of  Plot  M  there  was  a  change  in  the  direction 
of  the  canal,  and  at  that  point  a  considerable  amount  of  silt  and  other 
dlbris  had  collected.  This  debris  was  removed  from  the  ditch  every 
year  and  became  scattered  on  the  lower  half  of  plot  M.  Somewhat 
similar  conditions  existed  on  the  lower  half  of  plot  J. 


U 

Plot 

Manure 

Eureka 

covercrop 

Valencia 



Navel 

E 

D 

c 

B 

A 

Plot 

Navel 

Bone 

Potash 

Blood 

Check 

Cpmplet 

Valencia 

Eureka 

Lisbon 

J 

I 

H 

G 

F 

Plot 

Super 

Potash 

Sodiuri 
nltrat< 

Nitro- 
gen 
Bone 

Manure 

Navel 
Valencia 
Eureka 
Lisbon 

6 

H 

U 

L 

K 

Plot 

Manure 

Blood 

(i) 
Super 

Check 

Nitrogei 
Potash 

i  Bone 

Navel 

Valencia 

Eureka 

V 

Liabon 

T 

S 

R 

<k 

P 

Plot 

Manure 

Check 

Blood 

Potash 

Complet* 

Bone 

Havel 

covercrop 

Valencia 

Eureka 

Liabon 

H 

Eur.  Val.   Navel 
F'g-  2.— Diagram  showing  arrangement  of  plots  in  Rubidoux  fertilizer  trials. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  475 

The  land  just  below  the  fertilizer  experiment  block  was  cut  by 
several  old  gullies,  which,  at  the  time  of  planting  the  trees,  were 
almost  filled.  Three  of  these  gullies  extended  into  the  fertilizer  block. 
One  entered  the  lower  corner  of  plot  0,  one  ran  into  the  lower  part  of 
plots  S  and  R,  and  a  third  ran  up  through  the  lemons  in  plot  Q.  These 
gullies  were  filled  by  grading  in  from  the  land  immediately  around 
them.  A  considerable  amount  of  soil  was  doubtless  removed  from  the 
lower  part  of  plot  T,  the  southwest  part  of  plot  S,  the  southwest  part 
of  plot  R,  and  the  central  west  part  of  plot  Q. 

The  ground  slopes  with  a  fairly  steep  grade  from  northwest  to 
southeast.  The  soil14  is  not  entirely  uniform,  being  a  light  loam  at 
the  upper  end,  and  considerably  heavier  with  a  dense  subsoil  at  the 
lower  end.  Hardpan  is  to  be  found  at  present  close  to  the  surface  in 
the  lower  part  of  plot  T,  and  a  part  of  plot  V  has  been  left  out  of  the 
records  because  of  hardpan.    Nowhere  else  on  the  field  is  it  a  factor. 

The  trees  for  the  entire  orchard,  except  the  Lisbon  lemons,  were 
received  from  the  San  Dimas  Citrus  Nurseries  and  were  planted 
during  April  and  May  of  1907.  The  San  Dimas  trees  were  stored 
four  or  five  days  in  the  lath-house  before  shipping.  Upon  arrival, 
they  were  held  in  the  shade  of  some  eucalyptus  trees  and  kept  moist- 
ened until  all  were  planted.  They  were  irrigated  immediately  upon 
planting,  but  the  water  did  not  penetrate  well  into  the  balls.  New 
growth  was  thus  checked  somewhat,  but  a  few  days  later  the  balls  were 
broken  up  with  a  pick  and  the  trees  were  re-irrigated,  after  which  they 
made  a  vigorous  development  throughout  the  season.  The  Lisbon 
trees  were  obtained  from  the  Fancher  Creek  Nursery,  Fresno.  They 
were  smaller  than  the  San  Dimas  trees  and  did  not  make  so  good  a 
start  the  first  season. 

CARE  OF  THE  ORCHARD 

This  series  of  plots  was  laid  out  with  the  idea  of  testing  the  effect 
of  various  fertilizing  elements,  and  therefore  the  general  care  of  the 
orchard  has  been  kept  as  nearly  uniform  throughout  as  possible.  The 
attempt  has  been  made  to  maintain  a  good  dry  mulch  between  irri- 
gations through  the  summer  and  to  keep  the  moisture  conditions  as 
nearly  uniform  as  possible.  For  two  seasons  during  the  early  life 
of  the  experiment,  the  irrigation  water  was  run  from  north  to  south 
with  each  furrow  crossing  four  plots.  For  the  past  several  years, 
however,  and  during  the  time  when  the  larger  amount  of  fertilizer 

14  The  soil  on  this  tract  has  been  classified  as  Sierra  loam.  It  is  very  similar, 
agriculturally,  to  the  more  common  Placentia  loam,  and  doubtless  a  portion  of  it 
should  be  so  classified.  The  question  of  soil  types  for  citrus  is  discussed  at  some 
length  on  page  509  of  this  publication. 


476  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

has  been  used,  the  water  has  been  run  from  west  to  cast  and  has  been 
taken  off  as  waste  water  at  the  lower  end  of  each  plot.  Storm  water 
has  also  been  prevented  from  running  from  one  plot  to  another. 

During  the  first  five  years  of  the  experiment  a  winter  cover  crop 
of  barley  was  grown  on  all  of  the  20  original  plots.  (Plots  U  and  V 
had  leguminous  crops  during  this  period.)  This  barley  was  plowed 
under  each  year  in  the  spring.  Since  1912,  plots  A  to  T,  inclusive, 
have  been  clean  cultivated  throughout  the  year.  Plots  I'  and  V  have 
grown  a  leguminous  green  manure  crop  every  winter,  which  has  been 
plowed  down  in  the  spring;  these  plots,  like  all  the  others,  have  always 
been  clean  cultivated  through  the  summer. 

Comparatively  little  attention  has  been  paid  to  pruning.  So  far 
as  possible,  even  in  the  run-down  parts,  the  attempt  has  been  made  to 
treat  the  trees  as  nearly  alike  as  their  comparative  vigor  would  permit. 
Heavy  pruning,  as  also  attempts  to  renew  the  vigor  of  the  trees 
through  pruning,  has  in  no  case  been  resorted  to. 

IRRIGATION 

The  irrigation  practice  has  included  five  or  six  applications  during 
the  season,  commencing  generally  in  April  or  May  and  extending 
through  October.  Plots  U  and  V  have  received  one  more,  and  occa- 
sionally two  more  irrigations,  in  order  to  bring  the  cover  crop  along 
satisfactorily  in  the  fall  and  early  winter.  Four  furrows  are  used  to 
each  middle,  and  approximately  one-half  of  a  miner's  inch  is  used 
for  48  hours  in  the  four  furrows.  The  irrigation  runs  are  not  over 
200  feet  long,  and  the  intervals  between  irrigations  are  28  to  35  days. 

During  the  summer  of  1920  moisture  determinations  were  care- 
fully made  before  and  after  each  irrigation.  The  moisture  content 
was  reduced  to  the  theoretical  wilting  point  in  several  instances,  but 
on  the  whole  the  moisture  conditions  have  been  held  rather  uniform 
and  satisfactory  in  the  entire  field. 

DIFFERENTIAL  TREATMENTS 

These  field  trials  were  designed  especially  to  compare  the  effects 
on  citrus  tree  growth  and  production,  of  specific  fertilizers.  This  was 
somewhat  in  the  nature  of  pioneer  work,  for  no  one  element  of  plant 
food  was  then  recognized  as  the  principal  limiting  factor  in  citrus 
production.  Consequently,  one-clement,  two-element,  and  three- 
element  fertilizers  were  all  included  in  the  list  tested. 

On  each  of  the  plots  where  nitrogen  has  been  applied,  the  same 
total  amount  has  been  given  irrespective  of  the  source.     This  is  also 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  477 

true  of  the  plots  upon  which  phosphoric  acid  or  potassium  has  been 
used.  Certain  plots  have  been  treated  with  steamed  bone  only,  and 
such  plots  have  been  considered  phosphoric-acid  plots,  with  the  appli- 
cation governed  accordingly.  Some  nitrogen  has  necessarily  been 
carried  in  this  steamed  bone,  amounting  to  from  14  to  %  the  amount 
given  the  nitrogen-treated  plots.  One  of  the  superphosphate-treated 
plots  has  been  given  dried  blood  to  furnish  nitrogen  equal  in  amount 
to  that  contained  in  the  bone.  Certain  plots  have  been  fertilized  with 
stable  manure.  While  this  manure  has  not  been  analyzed  each  year, 
it  has  in  general  carried  about  the  same  amount  of  nitrogen  as  has  been 
applied  to  the  other  nitrogen-treated  plots.  Wherever  nitrate  of  soda 
has  been  used  with  organic  fertilizers  to  give  nitrogen,  it  has  supplied 
one-half  the  total  nitrogen.  The  following  outline  gives  the  type  of 
material  applied  to  each  plot. 

A.  Nitrate  of  soda,  blood,  bone,  and  sulfate  of  potash.      (Com- 

plete.)15 

B.  No  fertilizer. 

C.  Dried  blood. 

D.  Sulfate  of  potash. 

E.  Steamed  bone. 

F.  Stable  manure. 

G.  Nitrate  of  soda,  blood,  and  bone. 
H.  Nitrate  of  soda. 

I.    Muriate  of  potash.16 

J.  Superphosphate. 

K.  Steamed  bone  and  sulfate  of  potash. 

L.  Nitrate  of  soda,  blood,  and  sulfate  of  potash. 

M.  No  fertilizer. 

N.  Superphosphate  and  blood  to  equal  nitrogen  in  bone  plots.17 

0.  Stable  manure  and  rock  phosphate. 

P.  Steamed  bone. 

Q.  Nitrate  of  soda,  blood,  superphosphate,  and  sulfate  of  potash. 

(Complete.) 
R.  Sulfate  of  potash. 
S.  Dried  blood. 
T.  Unfertilized. 


is  By  common  usage,  a  fertilizer  containing  each  of  these  three  elements,  nitro- 
gen, phosphorus,  and  potassium,  is  considered  a  "complete  commercial  fertilizer." 
leSulfato  of  potash,  1920-1921. 
17  Blood  added  beginning  with  1914. 


DIVISION  OF  SUBTROPICAL  HORTICULTUT 
COLLEGE  OF  AGRICULTURE 


478  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

U.  Stable  manure,  rock  phosphate,  and  leguminous  cover  crop. 
(View-  atropurpurca,  Vicia  faba,  and  Melilotus  indica  have 
each  been  used  as  cover  crops  during  the  experiment.) 

V.  Stable  manure,  rock  phosphate,  and  leguminous  cover  crop. 

In  this  arrangement  several  of  the  treatments  have  been  duplicated 
and  a  few  of  them  triplicated.  Such  plots  are  grouped  together  in  the 
presentation  of  the  data.  In  certain  cases,  where  treatments  have  been 
closely  similar,  although  not  identical,  plots  have  been  considered 
duplicates  and  grouped.  The  following  combinations  are  thought  to 
be  entirely  justifiable  and  will  be  considered  as  contrasting  groups. 

Plots  Treatment 

U  and  V  Cover  crop  and  manure. 

F  and  0  Stable  manure. 

C  and  S  Dried  blood. 

A  and  Q  Complete  commercial  fertilizer. 

G  and  L  Nitrogen  and  one  other  element. 

H  Nitrate  of  soda. 

E,  K,  P  Steamed  bone. 

J  Superphosphate. 

D,  I,  R  Potash  only. 

B,  M,  T  No  fertilizer. 

The  distribution  of  the  plots  which  make  up  these  groups  may  be 
seen  by  referring  to  figure  2. 

Fertilization  of  the  trees  started  in  1907,  the  year  they  were 
planted,  with  relatively  small  amounts.  These  amounts  were  grad- 
ually increased  until  1914,  when  they  received  the  quantity  still  given 
annually,  which  is 

1.35  pounds  actual  nitrogen   per  tree. 

2.70  pounds  actual  phosphoric  acid  per  tree. 

1.35  pounds  actual  potash  per  tree. 

This  means  approximately  25  pounds  per  tree  of  5-10-5  formula 
fertilizer  (home  mixed)  on  the  complete  fertilizer  plots,  A  and  Q. 
10  pounds  per  tree  of  dried  blood  on  C  and  S. 
9  pounds  per  tree  of  nitrate  of  soda  on  H. 
14  pounds  per  tree  of  steamed  bone  on  E,  K,  P. 
2\  pounds  per  tree  of  sulfate  of  potash  on  D,  I,  R. 
13  pounds  per  tree  of  superphosphate  on  J. 
10  cubic  feet  per  tree  of  manure  on  plots  F  and  O. 
8  cubic  feet  per  tree  of  manure  on  plots  U  and  V. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES 


479 


YIELDS 

The  presentation  of  yield  data  in  a  comprehensive  and  at  the  same 
time  a  perfectly  fair  manner  is  recognized  to  be  difficult.  In  this  case 
a  table  (table  1)  is  given  which  shows  the  total  yield  for  each  indi- 
vidual plot  and  its  relative  position  in  the  field.  In  addition,  the 
plot  averages  are  given  in  pounds  per  tree  per  year  for  each  of  three 
periods  of  three  years  each  (table  2).  The  plots  that  are  treated  alike 
are  then  averaged  together  to  give  a  final  comparison  (table  3).  The 
graphs  have  been  prepared  to  illustrate  this  final  comparison  (fig.  3). 


1412.1414, inc. 

J  1  1   1  1   1  1  .  .  1 

i 

/9/«  -  IM2.0  inc. 

Ill.ll. 

1 

1.. 

1 

III 

lAlr 

1 

1£J 

ad 

ill 

1    1    1    .    1  . 

1Z34S(>783I0 
Key  /•  7>/<rf  ni/mfrers:- 

1.  U ,}/:  M*»ort  «n4  cai/trcrop. 

2.  T,0:  MiKurc. 

3.  C,S;Jr,<<l    3  load. 

4.  H    :    UitrcU  of  Soda.. 

5.  A,  CI-.  Cornptttt  Commereio.1. 
d.  (t,  L  :  fi'-<roaen  with  one 

other  element. 

Zf.K/P:  Stemmed  3«»«. 

8.1,  l/R  :  ?.ta.»h  . 

9.     T     :  Supcrj»h«iphate 

IO*.M,T:  l/»F«rt;fi*«i. 

£uzi 

I 

hi 

Li_ 

I 

1   1      

*Th»  I9lt  crop   <Mei    alme-it    a. 
t»mp/et«  fiil"rt   on  "-D    floti, 
iVih  t»  extreme  heal    in    Tune 
1917.     Th.s    it  refleel.4  In  the 
/•*    tJ|ree-year    «r»re.««. 

L 

id 

i?n: 

III 

.Ill    .    ., 

;    2 

5    " 

f  . 

f 

6 

7   8   . 

>  <o 

r    - 

t  . 

1    4  S    6   7    «    9  i° 

Fig.  3. — Rubidoux  trials.     Graphic  presentation  of  the  yields  by  groups  of 
plots.    Pounds  of  fruit  produced  per  tree  per  year,  averaged  by  three-year  periods. 


480 


1NIVKRSITY  OP  CALIFORNIA — EXPERIMENT  STATION 


TABLE  1 

Rubidoux  Trials 

Total  yield  in  pounds  per  tree,  averaged  for  each  plot. 

Nine  seasons  with  oranges,  1912-1920,  inclusive. 

Six  seasons  with  lemons,  1915-1920,  inclusive.* 


Plot 

Navel 

Valencia 

Eureka 

Lisbon 


1 

E 

D 

C 

B 

A 

Plot 

216 

36 

342 

36 

441 

Navel 

387 

90 

576 

36 

432 

Valencia 

169 

52 

400 

75 

340 

Eureka 

173 

21 

3% 

19 

209 

Lisbon 

J 

1 

H 

G 

F 

Plot 

72 

36 

252 

387 

378 

Navel 

279 

153 

234 

414 

837 

Valencia 

318 

162 

121 

269 

529 

Eureka 

256 

196 

171 

230 

726 

Lisbon 

0 

N 

M 

L 

K 

Plot 

378 

153 

90 

406 

252 

Navel 

756 

378 

225 

486 

576 

Valencia 

503 

305 

186 

268 

341 

Eureka 

800 

350 

180 

487 

366 

Lisbon 

V 

T 

S 

R 

Q 

P 

Plot 

423 

108 

522 

99 

603 

198 

Navel 

•Vis 

261 

756 

252 

630 

468 

Valencia 

630 

99 

500 

173 

530 

409 

Eureka 

39 

608 

92 

714 

535 

Lisbon 

•In  December,  1911.  and  January,  1913,  the  lemon  yields  were  seriously  affected  by  frost,  so  that 
no  data  are  submitted  prior  to  the  19)4-15  season. 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES 


481 


TABLE  2 
Rubidoux  Trials 
Yields  by  plots  in  pounds  per  tree(').     Average  for  year  by  three  year  periods. 


Plot 

Navel 

1912-1914 
Age  5,  6,  7 

Valencia 

Navel 

191.5-1917 
Age  8,  9,  10 

Valencia 

1918- 
Age  11 
Navel 

1920 
12,  13 

Valencia 

A 

36 

53 

67 

75 

39 

17 

B 

11 

9 

0 

3 

0 

1 

C 

34 

72 

63 

104 

24 

49 

D 

13 

12 

0 

17 

0 

1 

E 

41 

47 

31 

65 

0 

17 

F 

31 

53 

65 

128 

27 

98 

G 

29 

55 

70 

71 

30 

12 

H 

40 

59 

34 

17 

9 

1 

I 

11 

27 

0 

23 

0 

2 

J 

13 

33 

12 

49 

0 

10 

K 

31 

45 

45 

116 

2 

30 

L 

29 

57 

77 

77 

27 

26 

M 

20 

33 

10 

38 

0 

2 

N 

28 

36 

21 

66 

1 

24 

0 

28 

57 

73 

124 

24 

72 

P 

22 

44 

44 

91 

1 

16 

Q 

34 

52 

122 

130 

44 

24 

R 

24 

40 

9 

38 

0 

6 

S 

49 

56 

108 

135 

17 

62 

T 

27 

40 

9 

42 

0 

6 

U 

58 

95 

173 

146 

63 

138 

V 

36 

47 

75 

83 

30 

88 

(') — Lemon  yields  are  not  included  in  this  table  because  of  frost  injury  during  the  first  three-year 
period. 

TABLE  3 

Rubidoux  Trials 

Summary  of  yields  by  groups  of  plots. 

Average  annual  yield  per  tree  in  three-year  periods. 

ORANGES 


Group 

1912- 

-1914 

1915-1917 

1918-1920 

Treatment 

Navel 

Val. 

Navel 

Val. 

Navel 

Val. 

u,v 

27 

71 

124 

115 

46 

113 

Cover  crop  and  manure. 

F,0 

20 

55 

69 

126 

26 

85 

Manure. 

C,  S 

42 

64 

86 

120 

20 

56 

Dried  blood. 

H 

40 

59 

34 

17 

9 

1 

Nitrate  of  soda. 

A,Q 

35 

52 

94 

102 

42 

20 

Complete. 

G,  L 

29 

56 

74 

74 

28 

19 

Two  elements  with  nitrogen. 

E,  K,  P 

31 

45 

40 

91 

1 

21 

Steamed  bone. 

D,  I,  R 

16 

26 

3 

26 

0 

3 

Potash. 

J 

13 

33 

12 

49 

0 

10 

Superphosphate. 

B,  M,  T 

19 

27 

6 

28 

0 

3 

Unfertilized. 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 
COLLEGE  OF  AGRICULTURE 


482 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


LEMONS 


Eureka     Lisbon 

Eureka 

Lisbon 

Eureka 

Lisbon 

u,v 

184 

124 

F,  0 

139 

115 

33 

115 

c,s 

126 

99 

23 

68 

H 

40 

56 

0 

1 

A,Q 

134 

128 

9 

26 

G,  L 

85 

98 

4 

26 

K.  K.  P 

89 

90 

3 

31 

D,  I,  It 

40 

33 

3 

2 

J 

99 

34 

7 

2 

B,  M,  T 

37 

25 

2 

2 

ADDITIONAL    DATA 


Other  data  besides  yields  may  be  of  value  in  comparing  the  effects 
of  different  treatments.  The  following  table  gives  a  comparison  of 
fruit  quality  for  the  year  1914  and  for  the  Navel  crop  of  1921. 


TABLE  4 
RuBiDotrx  Trials 
Grade  a  d  Size  of  Fruit 


Groups  of  Plots 


%  Fancy  and  Choice 

%  Best  Sites 

1914 

1921 

1914 

1921 

u,v 

69 

80 

48 

54 

F,  O 

76 

75 

36 

52 

C,  8 

73 

78 

40 

34 

II 

73 

26 

35 

26 

A,Q 

74 

66 

44 

22 

G,  L 

78 

47 

39 

39 

D,  I,  K 

74 

* 

36 

* 

J 

72 

• 

43 

* 

B,  M,T 

71 

* 

33 

* 

•Not  sufficient  fruit  to  grade  or  siae. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  483 


Fig.  4. — Bubidoux  trials.     Typical  orange  tree  in  manure  and  cover-crop  plot. 
January,  1921.     (Compare  with  figs.  5  to  8.) 


484  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 


MOTTLE    LEAF 

Mottle  leaf  commenced  to  develop  early  on  certain  of  these  experi- 
mental plots.18  Coit  reports  indications  of  it  as  early  as  July,  1908, 
and  in  the  summer  of  1911  he  reported  that  the  differences  in  pro- 
duction of  the  young  Eureka  and  Valencia  trees  were  occasioned 
largely  by  the  amount  of  mottling  in  the  trees  in  the  various  plots. 
Mertz  reports  that  in  the  fall  of  1912  serious  mottling  was  confined  to 
the  Valencias  on  plots  H,  G,  and  A.  Following  the  freeze  of  January, 
1913,  a  notable  increase  in  mottling  was  observed.  This  was  at  first 
confined  to  plots  H,  A,  G,  L,  and  C,  but  gradually  appeared  on  all 
plots  fertilized  with  nitrogen  from  any  source.  By  1916. the  Eureka 
lemons,  showed  dying  back  of  twigs  on  plots  H,  A,  Gj  L,'  aad  C,  and 
in  1917  a  similar  condition  followed  mottling  on  the  Valencia  trees 
of  these  plots.  Since  1917  plot  H  (nitrate  of  soda)  has  produced 
practically  no  commercial  fruit. 


is  "  'Mottle-Leaf  is  a  term  applied  in  California  to  a  mottled  or  spotted  con- 
dition of  the  leaves  of  citrus  trees.  The  affected  portions  of  the  leaf  appear  to 
be  nearly  or  quite  devoid  of  chlorophyll  and  are  light  yellow  in  color.  In  the  first 
stages  of  the  disease  irregular  spots  several  millimeters  in  diameter  appear  between 
the  larger  veins,  usually  midway  between  the  midrib  and  the  margin.  The  half 
of  the  leaf  next  to  the  tip  is  often  first  affected.  In  the  more  advanced  stages, 
the  spots  are  larger  and  more  numerous,  until  finally  the  only  chlorophyll  remain- 
ing is  confined  to  the  midrib  and  the  larger  veins.  The  condition  is  distinguished 
from  what  is  generally  termed  'chlorosis'  by  the  fact  that  the  areas  surrounding 
the  yellowish  spots  retain  their  normal  green  color,  at  least  until  the  spots  embrace 
a  large  proportion  of  the  leaf.  The  term  'mottle-leaf  as  here  used  is  also  to  be 
understood  as  not  including  that  type  of  functional  disturbance  sometimes  found 
in  Citrus  leaves  in  which  the  midrib  and  veins  are  lighter  in  color  than  the 
surrounding  tissue. 

"Mottle-leaf  in  its  advanced  stages  is  accompanied  by  a  serious  reduction  in 
the  yield  and  in  the  size  and  quality  of  the  fruit.  The  foliage  becomes  thin  and 
weak  with  many  very  small  leaves;  and  the  ends  of  the  branches  have  a  brushy 
appearance,  owing  to  the  development  of  numerous  small  weak  twiga. " — Briggs, 
Jensen,  and  McLane,  Mottle  leaf  of  citrus  trees  in  relation  to  soil  conditions,  Jour. 
Agr.  Bes.,  vol.  6,  no.  19,  p.  721,  1916. 

Kelley  and  Cummins  have  stated,  as  a  result  of  studies  on  mottled  leaves  of 
citrus,  that  "Investigations  strongly  suggest  that  the  [mottled]  leaves  are  not 
suffering  from  inadequate  supplies  of  potassium,  phosphorus  or  nitrogen."  Kelley, 
W.  P.,  and  Cummins,  A.  B.,  Composition  of  normal  and  mottled  citrus  leaves, 
Jour.  Agr.  Bes.,  vol.  20,  no.  3,  p.  190,  1920. 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  485 


Fig.  5. — Kubidoux  trials.    Typical  orange  tree  in  manure  plot.    January,  1921. 


486  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

The  following  table  shows  a  careful  estimate  of  the  per  cent  of 
1  raves  showing  mottling  in  December,  1913,  November,  1914,  and 
December,  1920.    These  figures  are  an  average  of  all  varieties. 


TABLE  5 

Rubidoux  Trials 

Per  cent  of  leaves 

showing  mottling. 

Dec. 

Nov. 

Dec. 

Dec. 

Nov. 

Dec. 

1913 

1914 

1920 

1913 

1914 

1920 

A 

50 

70 

90 

N 

15 

20 

20 

B 

10 

25 

0 

O 

3 

8 

35 

C 

20 

50 

80 

P 

5 

20 

40 

D 

10 

20 

0 

Q 

5 

10 

85 

E 

10 

20 

60 

R 

10 

60 

10 

F 

5 

30 

40 

S 

5 

8 

60 

G 

50 

75 

95 

T 

10 

60 

10 

H 

80 

90 

100 

U 

2 

4 

20 

I 

20 

20 

0 

V 

1 

15 

5 

J 

40 

50 

20 

K 

5 

10 

35 

L 

60 

65 

85 

M 

50 

60 

0 

By  December,  1920,  plot  H  was  badly  killed  back  by  the  effects 
of  mottling.  Plots  A,  Q,  G,  L,  and  C  also  showed  markedly  injurious 
effects.  The  manured  plots  were  only  moderately  affected,  while 
the  plots  without  nitrogen  additions  showed  practically  no  typical 
mottling.    The  illustrations  bring  out  these  contrasts  fairly  well. 

DISCUSSION 

Certain  things  stand  out  clearly  from  the  data  submitted.  Under 
the  conditions  of  these  trials  there  can  be  no  question  but  that 

1.  Nitrogen  is  the  main  limiting  plant  food  element. 

2.  The  use  of  nitrogen  in  the  form  of  nitrate  of  soda,  and  to  a 
less  degree  in  the  form  of  dried  blood,  without  the  use  of  bulky 
organic  manure  of  some  sort,  is  conducive  to  the  development  of  mottle 
leaf  in  citrus  trees.  Following  the  continued  use  of  liberal  quantities 
of  these  materials  under  the  conditions  of  the  experiment,  mottling 
developed  to  a  point  where  certain  of  the  trees  were  rendered  entirely 
useless  from  the  production  standpoint. 

3.  Plots  to  which  no  nitrogen  was  applied  failed,  after  a  few  years, 
to  produce  any  crop  of  consequence.  Phosphoric  acid  and  potash, 
without  nitrogen,  produced  no  tree  or  fruit  conditions  different  from 
those  found  on  the  unfertilized  plots. 

4.  There  is  no  clear  evidence  that  phosphoric  acid  or  potash,  used 
in  conjunction  with  nitrogen,  has  bettered  the  amount  or  the  quality 
of  the  yield. 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  487 


■   ■■    ;j»>.'K 


Fig.  6. — Rubidoux  trials.     Typical  orange  tree  in  "complete"  fertilizer  plot. 
One-half  of  the  nitrogen  was  from  nitrate  of  soda.    January,  1921. 


DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


488  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

5.  Bulky  organic  manures  have  supplied  the  required  nitrogen 
and  at  the  same  time  have  limited  the  occurrence  of  mottling  as  com- 
pared with  the  commercially  fertilized  plots.  This  is  particularly 
noticeable  with  Valencias  and  Lisbons,  for  in  these  varieties  the 
manured  plots  have  produced  about  50  per  cent  more  fruit  than  the 
dried  blood  or  complete  fertilizer  groups. 

6.  "Winter  green-manure  crops,  in  conjunction  with  the  .use  of 
stable  manure,  have  given  better  results  in  increased  crop  yields  and 
improved  tree  conditions  than  have  come  from  the  use  of  stable 
manure  with  constant  clean  cultivation. 


II.    ARLINGTON  HEIGHTS  EXPERIMENT19 

PLAN    OF  THE    EXPERIMENTS 

Following  the  severe  freeze  of  January,  1913,  there  was  a  wide- 
spread feeling  that  many  of  the  older  citrus  groves  of  the  state  had 
passed  their  prime.  In  fact,  this  feeling  had  been  the  keynote  of  a 
State  Fruit-growers'  Convention  held  in  Pomona  as  early  as  July. 
1910.  In  response  to  this  feeling,  the  Citrus  Experiment  Station 
planned  and  instituted  a  field  trial  with  a  Navel  orange  grove,  designed 
to  test  out  various  methods  of  improving  a  run-down  grove.  The 
grove  selected  for  this  work  was  a  twenty-acre  block  of  old  Navels 
in  the  Arlington  Heights  section  of  Riverside,  planted  in  1891  on 
Placentia  loam  soil.  Treatments  were  begun  in  April,  1915,  and  were 
continued  to  April,  1920. 

The  deterioration  of  the  grove  at  the  time  these  trials  were  com- 
menced was  not  due  to  a  lack  of  fertilizer  applied  to  the  surface  of 
the  soil,  for  fairly  liberal  amounts  had  been  used  during  the  preceding 
ten  years ;  with  the  exception  of  the  one  year,  1914,  averaging  not  less 
than  90  pounds  nitrogen  per  acre  annually.  The  trouble  lay,  rather, 
in  recent  severe  frost  injury,  coupled  probably  with  poor  physical 
condition  of  the  soil.  This  latter  factor  evidenced  itself  especially  in 
the  difficulty  of  getting  the  ground  to  absorb  water  properly  at  the 
time  of  irrigation,  with  the  accompanying  inability  properly. to  dis- 
tribute the  fertilizer  materials  that  were  applied.  This  probably 
reacted  on  the  ability  of  the  trees  to  grow  sufficient  quantities  of  fiber 
roots  each  year.  During  the  six  years  preceding  the  frost  of  Decem- 
ber, 1911,  while  the  trees  were  from  16  to  22  years  old,  the  20  acres 

i»  For  other  accounts  of  these  trials  see  Vaile,  Calif.  Citrograph,  December, 
1920,  p.  44,  and  2d  Annual  Report  of  the  California  Citrus  Institute,  pp.  8-16, 
May,  1921. 


Bulletin  345]         fertilizer  experiments  with  citrus  trees  489 


Fig.  7. — Rubidoux  trials.    Typical  orange  tree  in  nitrate  of  soda  plot.    January, 
1921. 


490  INIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

averaged  approximately  five  field  boxes  of  fruit  per  tree  per  year. 
Even  during  this  period,  however,  a  considerable  development  of 
mottle  leaf  was  evident,  with  an  accompanying  tendency  toward  small 
leaves  even  when  of  good  color. 

In  March,  1915,  the  grove  was  in  lamentable  condition.  It  had 
not  been  pruned  at  all  since  the  freeze  and  was  full  of  dead  wood. 
What  new  growth  there  was,  was  almost  wholly  mottled.  The  yield 
was  not  over  a  quarter  of  a  field  box  to  the  tree  on  an  average,  and 
no  part  of  the  grove  gave  much  promise  of  rejuvenation. 

The  plan  of  the  trials  is  shown  in  the  accompanying  chart  (fig.  9). 
The  twenty  acres  was  divided  into  42  plots.  Plots  1  to  28  inclusive 
were  in  turn  divided  into  sub-plots  A  and  B,  each  of  which  contained 
nine  trees  completely  surrounded  by  guard  trees.  Plots  29  to  42 
inclusive  were  divided  into  three  sub-plots,  A,  B,  and  C. 

In  the  original  plan  of  the  trials,  certain  minor  differences  of  treat- 
ment were  not  repeated  frequently  enough  to  lend  much  confidence 
to  their  results.  No  attempt  is  made  in  this  report  to  draw  inferences 
from  such  cases.  These  include  the  comparison  between  manure 
used  with  and  manure  used  without  rock  phosphate,  the  comparison 
between  blood,  nitrate  of  soda,  and  sulfate  of  ammonia,  as  carriers 
of  nitrogen ;  the  application  of  manure  in  trenches  as  compared  with 
broadcasting,  the  use  of  summer  green-manure  crops  as  compared 
with  clean  summer  culture ;  shorter  than  normal  intervals  between 
irrigations;  extra  deep  plowing;  alfalfa  sod;20  and  alfalfa  hay21  as 
fertilizer. 


2°  Although  there  was  only  one  plot  seeded  to  alfalfa,  yet  the  results  were  so 
striking,  and  are  so  well  borne  out  by  other  instances  in  the  state,  that  a  general 
statement  seems  justified.  Alfalfa  was  planted  to  cover  the  entire  ground  except 
actually  under  the  trees.  The  plot  was  irrigated  once  every  two  weeks  throughout 
the  irrigation  season  and  at  no  time  did  the  trees  show  direct  evidence  of  lack  of 
moisture.  The  hay  was  cut  while  still  fairly  green,  and  was  piled  under  the  trees 
or  allowed  to  lie  where  it  foil.  Part  of  the  plot  was  supplied  with  nitrate  of  lime 
and  superphosphate.  The  trees  on  this  plot  showed  only  slight  improvement  the 
first  season,  and  from  then  on  they  show  marked  signs  of  deterioration,  including 
mottling,  sparse  foliage,  and  general  debility.  At  the  end  of  four  years  the  trees 
were  in  such  very  poor  condition  that  the  alfalfa  was  plowed  under  and  the  treat- 
ment discontinued.  It  does  not  seem  that  the  trouble  in  this  case  was  caused  by 
lack  of  plant  food,  for  the  sub-plot  fertilized  with  soluble  nitrogen  and  phosphates 
was  in  even  worse  condition  than  in  the  unfertilized  portion. 

si  The  plot  that  received  alfalfa  hay  showed  an  interesting  and  striking 
reaction  the  first  season.  One  hundred  and  fifty  pounds  of  hay  were  applied  per 
tree  and  plowed  under  in  the  spring  of  1915.  This  supplied  somewhat  over  300 
pounds  per  acre  of  rather  readily  available  nitrogen.  By  fall  the  trees  on  this 
plot  were  the  most  seriously  mottled  of  all  on  the  entire  tract,  with  90  per  cent 
of  the  leaves  affected.  In  following  years,  only  50  pounds  were  applied  each 
season  and  the  mottling  slowly  disappeared,  although  even  at  the  end  of  the  five 
years  this  plot  was  classed  as  moderately  mottled. 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  491 


Fig.  8. — Rubidoux  trials.  Typical  orange  tree  in  unfertilized  plot.  The  trees 
in  the  potash  and  phosphoric  acid  plots,  where  nitrogen  has  not  been  used,  show 
the  same  general  appearance.    January,  1921. 


492 


I   NIVKRSITY  OF  CALIFORNIA — KXPKRIMENT  STATION 


MOMIOI      ITBI1 


e 


s 

- 
e 

| 

B 
2 


S 
O 

3 

CO 

- 
£ 


I 

o 


«i= 


Hl» 


•I 


l- 


H- 


]«* 


III  =11 

*2*     J5~ 


•I 


iflij 


ll    , 


H 


iliill 


lA 


**1 

5r«  i 


tA     M 


■i 


x    2 


hfl 

sin* 


B-. 


I-l       el 

1*1  *  *J 


HJJ.JH 


ln«  J  I 


\A\ 
U 


h     * 


'M 


nil 


Lb 

•/.  ?  -  j. 


siitil 


ll 

°3 


hi 


islls 

&  °J' 


M 


lis  I 
IIS  1 


11-  J 

lis  1 


II 


■j 


lit  I 
111  * 

jlil 

1:!  6 

til  I 
1m  .1 
|3{|  ! 

lllj]     I 
h    ill 

•    *°N1   * 


ri 


8  .Si 


1   *.= 

3  I* 


i  ?tji 

2  hill  i  i 

£  Hilt     .* 
1  #,1  1  :« 


S    21 


a*  I  "a 

'-..gel 

£  •   s- 
|J"1* 

i*pj 


-  =  f  Sa 


bo 


2     I-  S 

—      3X  e 

m 

*&!'  a 

^3»  * 

•S-5-8?  I 

"    It  C 

15  E 

-  J! 


6£ 

l-*s  . 
fill  i 

*i»r?  ill*  ■ 

!  =  ,.«?      2»«^       9 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES 


493 


The  part  of  the  experiment  that  does  seem  of  real  value  is  the  com- 
parison of  three  groups  of  plots  between  which  the  essential  differences 
are  as  follows : 

Group  1.  Fertilized  with  commercial  fertilizer  high  in  nitrogen. 

Group  2.  Fertilized  with  stable  manure. 

Group  3.  Mulched  with  straw  completely  covering  the  ground. 

Each  of  these  groups  is  interspersed  with  unfertilized  plots  which 
are  used  as  checks  on  the  normal  production  of  its  portion  of  the  field. 
The  three  groups  of  plots  may  thus  be  compared  in  two  ways;  first, 
the  average  total  yield  per  tree  for  each  group ;  and  second,  the  in- 
crease in  yield  over  the  adjacent  checks.  The  following  diagram 
(fig.  10)  shows  the  arrangement  of  these  groups  with  their  accompany- 
ing checks. 


2 

/ 

/ 

6 

/ 

/ 

9 

10        11         12 

IJi         14 

1 

(| 

y 

26 

/ 

23 

22 

21 

2/6 

b|<      18      r 

n     -J, 

S"h 

/ 

30 

/ 

% 

35 

7 

37 

38    v.    y 

(      ,]        k2 

31 

32 

Fig.  10. — Arrangement  of  plots,  Arlington  Grove. 

1.  Commercial  fertilizer  plots :  12,  13,  16,  17,  19,  39,  41. 

Checks:  10,  14,  18,  38,  42. 

2.  Manure  plots:  9,  11,  21,  23,  35,  37. 

Checks:  6,  (1),  10,  18,  (1),  22,  34,  38. 

3.  Mulched  plots:  1,  4,  25,  27,  31,  32. 

Checks:  2,  6,  (1),  26,  30,  34,  (1). 

(1)  These  check  plots  are  given  only  one-half  value  because  of  their  location 
in  relation  to  the  particular  group  of  treated  plots  with  which  they  are  compared. 

In  addition  to  these  group  comparisons,  nearly  all  of  the  plots  not 
mulched  with  straw  were  clean  cultivated  throughout  the  year  on  sub- 
plot A  and  grew  a  winter  cover  crop  of  Melilotus  indica  on  sub-plot  B. 
This  gives  a  comparison  of  these  two  methods  of  culture  when  asso- 
ciated with  the  use  of  commercial  fertilizer,  stable  manure,  or  no  fer- 
tilizer. The  general  methods  of  culture  given  group  one  and  group 
two  were  essentially  similar  in  every  respect  except  as  to  the  fertilizer 
applied.  All  fertilizing  materials  were  spread  in  the  spring  and 
plowed  under. 


494 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


YIELDS 


The  yields  for  these  groups  of  plots,  by  individual  plots  and  group 
averages,  are  given  in  the  tables.  The  yields  of  the  checks  and  the 
increases  accompanying  the  different  treatments  are  represented 
graphically  in  figure  11. 


l*0_ 

140 


40  — 

J*— 


IH7 


I3H 


s 


1913 


i9*o 


.*<# 
-*»• 


—  30 

I* 


/.-  Cemrnftial    (crt  il  ikt  qroua    £  ~  MulehcJ  «roo.p     J-  Ma.T»«iTed  greu.0. 
T-     Tr4*tt«l    p|»tj  C-       An»mf**y<n*      cKteKl 

Fig.  11. — Arlington  experiment.     Yields  of  groups  of  plots  with  their  accom- 
panying checks. 

TABLE  6 
Arlington  Trials 
Total  yield  in  pounds  per  tree,  average  for  each  plot.     Five 
seasons,  1916  to  1920,  inclusive. 
Plots  shown  in  their  relative  positions  in  the  field. 


A 

810 

633 

667 

1059 

676 

518 

646 

553 

764 

496 

842 

779 

909 

330 

A 

Plots 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

Plots 

B 

967 

824 

756 

1074 

719 

468 

638 

514 

625 

503 

777 

780 

943 

523 

B 

A 

584 

875 

637 

684 

653 

591 

468 

649 

658 

752 

333 

772 

862 

746 

A 

Plots 

28 

27 

26 

25 

24 

23 

22 

21 

20 

19 

18 

17 

16 

15 

Plots 

B 

602 

841 

560 

839 

693 

473 

490 

464 

573 

729 

451 

814 

835 

552 

B 

A 

626 

526 

844 

648 

639 

470 

500 

608 

645 

494 

766 

844 

817 

495 

A 

Plot* 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

Plots 

B 

716|  442 

805  671 

568 

489J  524 

579 

509 

484 

624 

636 

705 

587 

B 

C 

601  448 

673  649 

564 

525  454 

599 

526 

408 

639 

584 

655 

620 

C 

Bulletin  345]         fertilizer  experiments  with  citrus  trees 


495 


TABLE 

7 

Average 

Annual  Yields  per  Tree 

Arlington  Experiment. 

Mulched  Plots 

1916 

1917 

1918 

1919 

19 

20 

Total 

Plot 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

1 

174 

136 

281 

276 

61 

56 

189 

250 

105 

249 

810 

967 

4 

115 

126 

205 

194 

195 

192 

261 

264 

283 

298 

1059 

1074 

25 

138 

135 

204 

226 

68 

69 

167 

235 

107 

174 

684 

839 

27 

128 

107 

200 

219 

175 

147 

186 

180 

186 

188 

875 

841 

31 

97 

70 

182 

167 

152 

153 

198 

210 

215 

205 

844 

805 

32 

105 

82 

118 

112 

108 

124 

200 

193 

117 

160 

648 

671 

Ave. 

126 

109 

198 

199 

126 

124 

200 

222 

169 

212 

820 

856 

Check  Plots 

2 

146 

155 

153 

178 

67 

77 

98 

165 

169 

249 

633 

824 

6* 

36 

38 

69 

55 

12 

13 

56 

50 

86 

78 

259 

234 

26 

141 

110 

119 

86 

83 

40 

136 

150 

158 

174 

637 

560 

30 

106 

93 

107 

62 

46 

14 

116 

131 

151 

142 

526 

442 

34* 

50 

43 

48 

38 

8 

8 

56 

68 

72 

88 

234 

245 

Ave. 

120 

110 

124 

105 

54 

38 

116 

146 

159 

183 

572 

576 

* 

(X%) 

Manure  Plots 

9 

151 

136 

203 

142 

25 

24 

150 

117 

235 

206 

764 

625 

11 

142 

144 

207 

194 

12 

36 

193 

141 

288 

262 

842 

777 

21 

131 

123 

135 

50 

37 

18 

145 

115 

201 

158 

649 

464 

23 

111 

90 

126 

55 

11 

7 

135 

133 

208 

188 

591 

473 

35 

103 

127 

55 

39 

17 

18 

150 

170 

175 

170 

500 

524 

37 

150 

117 

75 

35 

24 

17 

168 

157 

228 

183 

645 

509 

Ave. 

131 

123 

134 

86 

21 

20 

157 

139 

222 

195 

665 

562 

Check  Plots 

6* 

36 

38 

69 

55 

12 

13 

56 

50 

86 

78 

259 

234 

10 

149 

122 

167 

120 

6 

6 

59 

40 

115 

115 

496 

403 

18* 

64 

72 

51 

46 

1 

4 

6 

28 

45 

76 

167 

226 

22 

110 

128 

111 

83 

21 

i6 

87 

121 

139 

142 

468 

490 

34 

101 

86 

97 

76 

16 

15 

112 

137 

144 

175 

470 

489 

38 

173 

152 

89 

65 

5 

11 

45 

102 

82 

154 

394 

484 

Ave. 

127 

120 

117 

89 

12 

13 

73 

96 

122 

148 

451 

465 

• 

(X%) 

Chemical  Fertiliser  Plots 

12 

162 

152 

171 

162 

43 

71 

173 

156 

250 

239 

799 

780 

13 

176 

183 

197 

188 

98 

111 

190 

199 

248 

262 

909 

943 

16 

194 

188 

174 

147 

79 

100 

193 

185 

222 

215 

862 

835 

17 

197 

212 

107 

149 

115 

74 

160 

166 

193 

213 

772 

814 

19 

146 

172 

137 

105 

112 

113 

154 

152 

203 

187 

752 

729 

39 

203 

169 

106 

70 

89 

46 

186 

157 

182 

182 

766 

624 

41 

200 

169 

99 

97 

95 

50 

189 

171 

234 

218 

817 

705 

Ave. 

182 

179 

142 

131 

90 

81 

178 

169 

219 

217 

811 

776 

DIVISION  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


496 


I'NIVKRSITY  OF  CALIFORNIA — EXPKRIMKXT  STATION 


Cheek  Plot* 

TABLE  7 

—  (Continued) 

1916 

191 

17 

1918 

1919 

19: 

50 

Total 

Plot 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

A 

B 

10 

149 

122 

167 

120 

6 

6 

59 

40 

115 

115 

496 

403 

14 

129 

183 

137 

152 

3 

7 

32 

77 

29 

104 

330 

523 

18 

127 

144 

102 

91 

8 

7 

13 

57 

89 

152 

333 

451 

38 

173 

152 

89 

65 

5 

11 

45 

102 

82 

154 

394 

484 

42 

137 

136 

83 

99 

18 

14 

85 

133 

172 

205 

495 

587 

Ave. 

143 

147 

116 

105 

7 

9 

47 

82 

97 

146 

410 

489 

Unfertilized  Plots 

2 

146 

165 

153 

178 

67 

77 

98 

165 

169 

249 

633 

824 

6 

71 

75 

138 

110 

23 

86 

112 

99 

172 

157 

518 

468 

10 

149 

122 

167 

120 

6 

6 

59 

40 

115 

115 

496 

403 

14 

129 

183 

137 

158 

3 

7 

32 

77 

29 

104 

330 

523 

18 

127 

144 

102 

91 

2 

7 

13 

57 

89 

152 

333 

451 

22 

110 

128 

111 

83 

21 

16 

87 

121 

139 

142 

468 

490 

26 

141 

110 

119 

86 

83 

40 

136 

150 

158 

174 

637 

560 

30 

106 

93 

107 

62 

46 

14 

116 

131 

151 

142 

526 

442 

34 

101 

86 

97 

76 

16 

15 

112 

137 

144 

175 

470 

489 

38 

173 

152 

89 

65 

5 

11 

4.1 

102 

82 

154 

394 

484 

42 

137 

136 

83 

99 

18 

14 

85 

133 

172 

205 

495 

587 

Ave, 

126 

127 

118 

102 

27 

17 

81 

110 

129 

161 

482 

520 

MOTTLE    LEAF 

At  the  end  of  five  years,  there  existed  differences  in  the  appear- 
ance of  the  trees,  which  wen-  not  entirely  reflected  by  the  yields, 
although  it  seems  highly  probable  that  they  would  have  been  had  the 
trials  been  continued  for  a  few  more  years.  Careful  estimates  were 
made  of  the  mottling  in  December.  1916.  and  December,  1919,  the 
results  of  which  are  given  in  table  8. 


TABLE  8 

Mottle  Leat,  by  Groups  ok  Plots 

Class  I  with  loss  than  11%  mottled  leaves.     Good  condition. 
Class  II  with   11-20%  mottled  leaves.     Slightly  mottled, 
(lass  III  with   21-30%    mottled   leaves.     Moderately   mottled. 
Class  IV  with  31-40%  mottled  leaves.     Badly  mottled. 
Number  of  plots  from,  each  group   Hint  fall  into  each  class. 


Chem.  Fcrt. 
(7   plots) 

1916 
1919 

Clawi  I 

1 

i  I..-  II 
4 

ClftU  III 

2 
2 

Mulched 
(6  plots) 

1916 
1919 

1 

3 

2 

Manured 
(13  plots) 

1916 
1919 

7 
6 

5 
6 

1 

Unfertilized 
(11  plots) 

1916 
1919 

8 
8 

3 
2  ' 

1 

Claw  IV 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  497 


Fig.  12. — Arlington  trials.    Typical  tree  in  manure  group  of  plots.     December, 
1919. 


498  UNIVERSITY  OP  CA1JFORN1A — EXPERIMENT  STATION 

DISCUSSION 

The  outstanding  points  of  behavior  in  this  experiment  are  the  fol- 
lowing : 

1.  There  was  a  decided  response  to  the  application  of  chemical 
fertilizers  applied  in  April,  1915,  as  measured  by  the  crop  harvested 
in  March,  1916.  No  other  treatment  gave  any  significant  increase  the 
first  season. 

2.  There  was  a  continued  increase  of  crop  in  response  to  chemical 
fertilizers  throughout  the  five  years.  This  was  accompanied,  however, 
by  an  increase  in  mottling. 

3.  Immediately  following  the  extremely  hot  weather  of  June,  1917, 
the  commercial-fertilizer  plots  and  the  mulched  plots  were  the  only 
ones  that  did  not  drop  practically  all  of  their  young  fruit. 

4.  The  mulched  plots  showed  striking  increases  during  the  second, 
third,  and  fourth  years  of  the  trials,  but  by  the  fifth  year  they  were 
so  seriously  affected  with  mottle  leaf  that  the  crop  was  materially 
reduced.  So  pronounced  was  the  final  effect  and  so  in  keeping  is 
it  with  growers'  experiences  elsewhere  in  southern  California,  that 
mulching  does  not  seem  a  possible  method  to  employ  permanently  on 
soils  similar  to  that  at  Arlington.  It  may,  however,  be  of  much  value 
for  two  or  three  years. 

5.  The  manured  plots  responded  very  slowly  to  the  spring  appli- 
cations of  manure,  but  at  the  close  of  the  five  years  they  were  yielding 
as  well  as  any  other  group  and  the  trees  showed  more  vigor  and  better 
color  than  those  of  any  other  group.  Estimates  made  of  the  1921 
crop,  after  the  experiment  had  been  abandoned  (no  fertilizer  was 
applied  during  1920),  indicated  that  the  manured  plots  would  yield 
about  20  per  cent  more  fruit  per  tree  than  the  chemical-fertilizer 
group,  and  40  per  cent  more  than  the  mulched  group. 

6.  Under  the  conditions  of  these  trials,  the  increases  in  crop  yield 
accompanying  the  different  group  treatments  were  obtained  at  much 
less  cost  on  the  chemical-fertilizer  group  than  on  either  of  the  others 
when  the  full  five-year  period  is  considered.  When  the  1920  crop 
alone  is  considered,  the  difference  in  favor  of  the  chemical  fertilizer 
group  in  comparison  with  the  manured  group  is  much  less. 

The  mere  cost  of  the  fertilizer  and  of  the  other  materials  when 
charged  to  the  increase  in  crop  yield  on  the  treated  trees  compared  to 
the  adjacent  checks  was  as  follows: 

Cost  of  special  treatment  for  each 
pound  of  increased  yield 
Total  5  years  1920 

Chemical  fertilizer  group 0.7  cents  0.43  cents 

Mulched  group  1.4  cents  5.00  cents 

Manure  group  _ 1.6  cents  0.63  cents 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  499 


Fig.  13. — Arlington  trials.    Typical  tree  in  commercial  fertilizer  group  of  plots. 
December,  1919. 


UV.S.0N  OF  SUBTROPICAL  H0R1OU 
COLLEGE  OF  AGRICULTURE 
BERKELEY,  CALIFORNIA 


;-><X 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


Ki>j.  14. — Arlington  trials.     Typical  tree  in  mulched  group  of  plots.     December, 
1919. 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  501 

7.  The  use  of  winter  green-manure  crops  has  shown  no  particular 
advantage  on  any  of  the  fertilized  plots,  no  matter  what  the  source 
of  fertilizer.  On  the  manured  plots  the  yields  have  been  distinctly 
less  where  cover  crops  were  grown  than  where  the  land  was  given  clean 
culture.  It  has  not  been  possible  to  analyze  the  reasons  for  the  lack 
of  benefit  from  cover  cropping  in  this  case,  especially  in  view  of  the 
markedly  favorable  effect  of  cover  crops  indicated  by  the  Rubidoux 


ait 


>ai* 


-Ito 
-lie 


/-  £omwiTCiai  Fertilizer  orou.p    2  -  Manured  qroup     J.-  Urtfe-rM. zed  <jrou.p 

Fig.  15. — Arlington  experiment.     Diagram  showing  effect  of  cover 


crop. 


trials.  The  growth  of  the  cover  crop  has  consistently  been  highly 
successful ;  neither  the  cover  crop  nor  the  trees  ever  showed  indication 
of  lack  of  water ;  the  land  both  in  clean  culture  and  in  cover  crop  was 
all  plowed  at  the  same  time  and  to  the  same  depth  each  spring.  On 
the  unfertilized  plots  cover  crops  had  a  slightly  depressing  effect  in 
the  second  and  third  years,  but  during  the  last  two  years  of  the  trial 
they  seemed  to  be  of- marked  benefit.  This  benefit  was  not  sufficiently 
great,  however,  to  make  the  cover  cropped  portion  of  the  unfertilized 
plots  commercially  successful.  The  effect  of  cover  crops  is  shown 
graphically  in  figure  15. 


2X0358 


502  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 

8.  Throughout  the  period  of  the  trials  the  fruit  of  best  quality  was 
produced  on  the  plots  fertilized  with  dried  blood.  Second  to  this  was 
the  fruit  produced  on  the  manured  plots.  In  both  cases  the  average 
quality  was  high.  Apparently  applications  of  phosphoric  acid  and 
potash  are  not  essential  for  the  production  of  high  quality  fruit,  under 
the  conditions  of  these  trials. 


III.     CHAFFEY  EXPERIMENT22 

PLAN    OF    THE    EXPERIMENTS 

Another  trial  with  an  old  Navel  grove  was  located  on  the  orchard 
belonging  to  the  Chaffey  Union  High  School  at  Ontario.  This  grove 
was  planted  in  1899.  The  soil  is  Hanford  gravelly  loam.  The  trial 
plots  were  outlined  by  the  writer  in  collaboration  with  C.  J.  Booth 
of  the  Chaffey  Union  High  School  and  Junior  College.  Treatments 
were  first  begun  in  1915. 

There  are  approximately  six  acres  included  in  the  experiments. 
Five  fertilizer  treatments  are  applied  in  plots  four  trees  wide  by 
twenty-eight  trees  long.    The  treatments  consist  of: 

1.  Stable  manure,  6VL>  cubic  feet  per  tree.23 

2.  "Complete"  fertilizer,  5-9-1  y2,  14  lbs.  per  tree,  giving  0.7  lb. 

actual  nitrogen  per  tree  (2  per  cent  of  nitrogen  inorganic, 
and  3  per  cent  organic.) 

3.  Tankage,  8-8,  13V2  lbs.  per  tree, — 1  lb.  actual  nitrogen  per  tree. 

4.  Ammonium  sulfate,  9  lbs.  per  tree, — 2  lbs.  actual  nitrogen  per 

tree. 

5.  Cottonseed  meal,  15  lbs.  per  tree, — 1  lb.  actual  nitrogen  per  tree. 

Crossing  these  five  fertilizer  plots,  four  cultural  treatments  were 
installed,  as  follows : 

A.  Winter  green  manure. 

B.  Winter  green  manure  and  2y2  tons  ground  limestone  per  acre 
per  year. 

C.  Clean  culture  all  year. 

D.  Mulched  with  straw. 

Each  of  these  plots  is  seven  trees  long  by  twenty  trees  wide,  and 
crosses  all  the  fertilizer  plots  equally. 

*»  For  other  accounts  of  this  experiment,  see  Booth,  C.  J.,  Bull.  No.  3,  Dept. 
of  Agrie.,  Chaffey  Union  High  School,  and  Booth,  California  Citrograph,  vol.  4, 
no.  8,  p.  205,  June,  1919. 

**  The  amounts  of  fertilizer  used  in  these  trials  were  originally  based  on  a  unit 
cost  per  tree,  rather  than  on  the  amount  of  plant  food  contained. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  503 

When  the  trials  were  commenced,  the  grove  was  badly  run  down, 
having  been  neglected  for  some  time.  No  fertilizer  had  been  applied 
for  several  years  and  the  trees  were,  in  consequence,  considerably 
yellowed  with  sparse  foliage.  Irrigation  water  had  been  applied  in 
furrows  600  feet  long  at  intervals  of  30  days,  with  the  result  that  the 
light  soil  at  the  upper  end  of  the  grove  (sub-plot  A)  had  been  leached 
of  much  of  its  plant  food,  while  the  trees  in  sub-plots  C  and  D  had 
evidently  suffered  from  lack  of  water  at  times.  To  remedy  these 
conditions,  an  auxiliary  pipe  line  was  installed  at  the  head  of  sub- 
plot C  and  the  irrigation  interval  was  reduced  to  14  days.  One  and 
a  quarter  acre-inches  of  water  were  applied  at  each  irrigation. 

In  contrast  to  the  Arlington  plots,  mottle  leaf  was  not  a  serious 
problem  on  this  grove  at  the  beginning  of  the  trials.  Lack  of  available 
plant  food  seemed  to  be  the  principal  limiting  factor.  Sub-plot  A 
was  very  much  poorer  in  the  beginning  than  ony  of  the  others,  and 
should  hardly  be  compared  with  the  balance  of  the  orchard,  even  yet. 
The  rest  of  the  grove  was  uniform. 

The  diagram  (fig.  16)  shows  the  arrangement  of  the  plots  and 
the  treatments,  together  with  the  total  six-year  yield.  The  yield  per 
year  is  shown  in  table  9. 


DISCUSSION 

1.  The  striking  increase  in  the  1921  yield  over  any  previous  yield 
is  the  outstanding  point  in  the  experiment.  The  evidence  is  very 
clear  that  a  badly  run-down  grove  can  be  brought  back  into  heavy 
bearing  only  after  several  years  of  good  care. 

2.  Analysis  of  the  1916  and  1917  yields  shows  that  the  plot  receiv- 
ing the  more  readily  available  nitrogen  in  the  form  of  sulfate  of 
ammonia  responded  only  slightly  more  quickly  than  the  one  receiving 
cottonseed  meal,  but  the  sulfate  of  ammonia  plot,  with  2  pounds  of 
actual  nitrogen  per  tree,  did  give  a  considerably  better  yield  in  1917 
than  the  "complete"  fertilizer  plot,  with  only  .7  pound  actual  nitro- 
gen per  tree.  This  indicated  that  the  amount  of  nitrogen  was  of  more 
importance  for  the  first  year  than  the  kind  of  fertilizer. 

3.  On  the  other  hand,  the  yields  in  the  later  years  (1920  and  1921) 
were  no  greater  with  the  2  pounds  of  nitrogen  per  tree  than  on  the 
plots  given  1  pound  or  .7  pound  of  nitrogen. 

4.  The  total  six  year  yields  on  the  five  fertilizer  plots  are  certainly 
within  the  range  of  natural  variation  for  such  trials. 


504 


t  MVKKSITY  OF  CALIFORNIA — EXI'KRIMKNT  STATION 


5.  The  mulched  plot  has  consistently  shown  a  marked  superiority 
over  any  of  the  other  cultural  plots.  This  superiority  was  in  evidence 
as  early  as  1917  and  was  most  pronounced  in  1919. 

6.  Mottle  leaf  commenced  to  appear  on  the  mulched  plots  early  in 
1919.  By  February.  L921,  it  was  recognized  as  a  serious  factor,  par- 
ticularly in  sub-plots  Id  and  2d.  As  the  mottle  leaf  increased,  the 
superiority  of  the  mulched  plot  diminished.  In  1921  mottle  leaf  had 
also  developed  to  some  extent  throughout  the  sulfate  of  ammonia  plot, 
and  especially  in  the  clean  cultivated  portion. 

7.  The  six  year  average  yield  on  the  cover  cropped  area  of  all  the 
plots  together  is  identical  with  the  yield  on  the  clean  cultivated  area. 
The  high  value  of  organic  material  is,  however,  strongly  indicated  in 
the  sulfate  of  ammonia  plot,  where  the  sub-plot  in  which  cover  crops 
have  been  grown  is  markedly  superior  in  yield  and  appearance  to  the 
clean  cultivated  sub-plot.  The  exact  reverse  of  this  condition  exists 
in  the  "complete"  fertilizer  plot,  one  reason  for  which  would  seem 
to  be  the  relatively  small  applications  of  nitrogen,  which  may  not  have 
been  sufficient  for  both  trees  and  cover  crop  during  certain  critical 
periods. 


Pert  in- 
ter 
Plot 


V.anure 


Avcragei 


516 


Complete   Tankage 


Sulfate  of  Cottonoeed 
ammonia    meal 


1 

.   2 

r   * 

1, 

5 

370 

Ul8 

362 

518 

35U 

Sub-plot 

A  • 
cover-crop 

l,n7 

U57 

U25 

U99 

531 

58U 

B 
covcrcrop 
lime 

5Uo 

502 

U60 

U56 

589 

C 
Clean 
Culture 

72U 

796 

710 

710 

611 

D 
Mulch 
70Q 

523 


5<* 


5U8 


5U2 


Fig.  16. — Chaffey  Experimental  Grove.  Diagram  showing  arrangement  of 
plota  and  average  total  yield  in  pounds  per  tree  for  six  seasons,  1916-1921,  inclu- 
sive. 


WYISK)N  OF  SUBTROPICAL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  50;') 


TABLE  9 
Chaffey  Grove,  Average  Yields  in  Pounds  per  Tree. 
Six  Year  Summary 


1916 

1917 

1918 

1919 

1920 

1921 

Total 
6yrs. 

1A    Manure 

00 

7 
2 
0 
1 

63 
52 
61 
99 

58 

14 
9 

00 
5 
0 

91 
94 
80 
100 
92 

44 
81 
65 
107 
80 

158 
175 
154 
207 
158 

370 

2A    Complete 

418 

Covercrop 

3A    Tankage 

362 

4A    Sul.  Am 

518 

5A    Cottonseed  meal 

419 

All  A 

2 

67 

1 

91 

76 

170 

407 

IB    Manure 

4 
1 
1 
3 
2 

98 

54 

76 

125 

126 

6 
0 
0 
0 
0 

103 

111 
106 
103 
120 

64 
76 
73 

98 
112 

182 
183 
243 
202 
224 

457 

Covercrop 

2B    Complete 

425 

Lime 

3B    Tankage 

499 

4B    Sul.  Am 

531 

5B    Cottonseed  meal 

584 

A11B 

2 

96 

1 

109 

85 

207 

500 

1C    Manure 

13 
16 
12 

4 

8 

95 

63 

98 

138 

162 

2 
0 
0 
2 
0 

101 
84 
35 
45 
80 

108 

131 

101 

65 

96 

221 
208 
214 
202 
243 

540 

Clean 

2C    Complete 

502 

Culture 

3C    Tankage 

460 

4C    Sul.  Am 

456 

5C    Cottonseed  meal 

589 

A11C 

10 

111 

1 

69 

100 

218 

507 

ID   Manure 

24 
30 

22 
21 
12 

125 

94 

91 

167 

123 

76 
108 
38 
41 
12 

175 
212 
174 
148 
110 

122 
123 
120 
135 
115 

202 
229 
265 
198 
239 

724 

2D   Complete 

796 

Mulched 

3D   Tankage 

710 

4D  Sul.  Am 

710 

5D   Cottonseed  meal 

611 

A11D 

22 

120 

55 

162 

123 

227 

709 

1.      Manure 

9 
12 
8 
6 
6 

95 

66 

81 

132 

117 

18 

18 

7 

8 

2 

118 

125 

99 

99 

100 

85 
103 

90 
101 
101 

191 
199 
219 

■202 
216 

516 

2.  ComDlete 

3.  Tankage   

523 
504 

4.      Sul.  Am 

5      Cottonseed  meal 

548 
542 

DIVISION  OF  SUbtROPICAl  HORTICULTURE 

COLLEGE 'OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


506  UNIVERSITY  OP  CALIFORNIA — EXPERIMENT  STATION 


ADDITIONAL  GROWERS'  TRIALS 

In  1914  Vaile  reported24  the  results  of  three  growers'  field  trials, 
located  respectively  in  Yolo  silt  loam  near  Santa  Paula,  Placentia 
loam,  at  Riverside,  and  Hanford  gravelly  loam  soil,  at  Pomona,  two 
of  which  showed  unmistakable  results  from  the  use  of  nitrogenous  fer- 
tilizers, but  were  without  noticeable  results  following  the  use  of  potash 
or  phosphoric  acid.  The  third  trial,  designed  merely  to  test  the  effect 
of  potash,  was  entirely  negative  in  results. 

A  field  trial  with  the  use  of  nitrogenous  fertilizers  was  conducted 
by  a  grower  of  lemon  trees  on  Yolo  gravelly  light  sandy  loam  soil  near 
Santa  Paula,  beginning  in  1914  when  the  trees  were  seven  years  old. 
A  vigorous  winter  cover  crop  was  grown  every  year,  and  in  addition 
fairly  liberal  applications  of  dried  blood,  manure,  and  sulfate  of 
ammonia  were  used.  Two  middles,  completely  surrounding  one  row 
of  36  trees,  were  left  without  fertilizer  of  any  sort  except  the  cover 
crop,  for  five  subsequent  years,  during  which  time  they  produced  an 
average  of  8.3  field  boxes  of  lemons  per  tree  annually,  while  the  first 
fertilized  row  adjoining  produced  an  average  of  9.6  field  boxes. 

An  orange  grove  located  on  Hanford  gravelly  sandy  loam  near 
Pomona,  was  fertilized  with  nitrate  of  soda,  superphosphate,  and 
tankage,  for  the  five  years  of  1911-1915  inclusive.  One  strip  through 
the  grove  was  supplied  with  sulfate  of  potash  at  the  rate  of  two 
pounds  per  tree  annually  throughout  this  period.  There  was  no  meas- 
urable difference  following  the  use  of  potash. 

In  another  case  on  Yolo  loam  soil  near  Fillmore,  six  adjoining  plots 
of  lemons  were  laid  out  in  1911.  Five  were  fertilized  respectively 
with  sodium  nitrate,  dried  blood,  ammonium  sulfate,  tankage,  sodium 
nitrate,  and  superphosphate,  while  one  was  left  unfertilized. 

In  1917,  after  these  treatments  had  been  continued  for  seven  years, 
the  unfertilized  trees  could  be  picked  out  by  observation,  but  the 
increased  yields  had  hardly  paid  for  the  fertilizer  applications.  There 
was  no  measurable  difference  in  tree  growth,  yield,  or  fruit  quality, 
between  the  variously  fertilized  plots. 

A  growers'  cooperative  field  trial  at  Chula  Vista,  with  young  lemon 
trees  planted  in  1915  on  Kimball  sandy  loam  soil,  was  outlined  by  the 
writer  and  conducted  from  1915  to  1920  inclusive.  Lemon  trees  had 
previously  grown  on  this  land  for  at  least  20  years,  but  the  young 

2*  I'rocff<liiiKH  of  the  45th  California  State  Fruit  Growers'  Convention,  Los 
Angeles,  Nov.  10-14,  1914,  p.  135. 


BULLETIN  345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  507 

trees  were  not  planted  in  the  holes  from  which  the  lemon  trees  were 
removed.  There  were  five  major  plots,  each  comprising  four  rows  of 
thirty  trees,  with  unfertilized  guard  rows  surrounding  each  plot. 
Each  of  these  major  plots  was  crossed  by  secondary  treatments  so  that 
the  plots  were  divided  into  four  sub-plots,  designated  as  A,  B,  C,  D. 
The  treatments  were  as  follows : 

Plot  1                Plot  2                  Plot  S  Plot  4                 Plot  5 

Basined  and     Fertilized             Fertilized  Fertilized            Fertilized 

mulched.            with  complete      with  sulfate  with  dried          with  stable 

fertilizer.             of  ammonia.  blood.                  manure. 
Sub-plot  A.     Clean  cultivated. 
Sub-plot  B.     Winter  cover  crop. 
Sub-plot  C.     Winter  cover  crop  and  superphosphate. 

Sub-plot  D.     Winter  cover  crop  and  ground  limestone. 

At  the  end  of  the  second  year  the  unfertilized  guard  rows  were 
easily  distinguishable  because  of  lighter  colored  foliage  and  shorter 
growth. 

At  the  end  of  the  third  year,  the  basined  and  mulched  trees  were 
distinctly  the  largest  of  all  on  the  tract.  The  trees  fertilized  with  sul- 
fate of  ammonia  were  second  in  size  and  had  darker  colored  foliage 
than  any  others.  By  this  time  the  inferiority  of  the  unfertilized  trees 
was  so  pronounced  that  sulfate  of  ammonia  was  subsequently  applied 
to  all  of  them. 

At  the  end  of  the  fifth  year  the  average  total  yield  from  the  several 
plots  was  as  follows : 

Yield  in  field 
Plot  boxes  per  tree 

Mulched   basined  _ 5 

Sulfate  of  ammonia 4.5 

Dried  blood  3.0 

Complete   3.0 

Manure    2.2 

Orchards  adjoining  on  three  sides,  planted  at  the  same  time,  but 
unfertilized  the  first  four  years,  had  yielded  practically  no  fruit  to 
the  same  date. 

None  of  the  sub-plots  showed  any  significant  differences  except 
that  the  use  of  lime  seemed  to  make  an  increased  growth  on  plots  2, 
3,  and  4,  when  compared  to  the  superphosphate  sub-plots  immediately 
adjoining.  This  is  the  only  case  in  any  trial  noted  where  lime  seems 
to  have  been  a  factor  in  increasing  growth. 

A  somewhat  similar  trial  planned  by  the  writer  was  conducted 
from  February,  1916,  to  date,  with  Navel  oranges  planted  in  1907  on 


508  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

San  Joaquin25  loam  soil,  near  Naranjo,  Tulare  County.     There  were 
four  major  plots,  each  divided  into  four  sub-plots  as  follows : 


Plot  1 

Plot  g 

Plot  3 

Plot  4 

Fertilized 

Fertilized 

Fertilized 

Fertilized 

with  nitrate 

with  8-8 

with  4-10-2 

with  stable 

of  soda. 

tankage. 

complete  fertilizer. 

manure. 

Sub-plot  A. 

Winter  cover 

crop. 

Sub-plot  B. 

Winter  cover 

crop  and  lime. 

Sub-plot  C. 

Clean  culture. 

Sub-plot  D. 

Mulched. 

There  are  no  outstanding  differences  between  these  plots  except 
(1)  all  of  the  mulched  sub-plots  showed  a  marked  increase  the  first 
year,  but  owing  to  local  drainage  difficulties  and  gopher  injury,  the 
significance  of  this  treatment  was  soon  lost.  How  long  the  increase 
would  have  continued  is  therefore  not  known.  (2)  The  manured  plot 
seems  to  show  the  greatest  total  improvement  to  date  as  manifested 
by  the  1920  crop  and  the  present  condition  of  the  trees. 

All  these  trials  indicate  that  fertilization  with  nitrogenous  mater- 
ials has  a  positive  effect  on  citrus  fruit  production,  but  that  fertil- 
ization with  phosphoric  acid  and  potash  usually  does  not  have  any 
measurable  effect.  There  is  little  or  no  real  evidence  from  any  of 
these  trials  regarding  the  kind  of  nitrogenous  fertilizer  or  the  amount 
that  may  be  expected  to  give  the  best  results. 


CALIFORNIA   CITRUS   SOILS 

The  field  trials  with  fertilizer  on  citrus  trees  discussed  above  are 
located  on  various  types  of  soil.  It  has  often  been  said  that  soil  types 
have  a  great  deal  to  do  with  fertilizer  practice  and  its  results.  With 
these  points  in  mind  the  following  brief  description  is  appended  to 
the  consideration  of  citrus  fertilization.  A  large  part  of  the  material 
presented  is  summarized  from  the  reports  of  the  soil  surveys  con- 
ducted jointly  by  the  U.  S.  Bureau  of  Soils  and  the  College  of  Agri- 
culture. The  convenience  of  such  a  summary  for  reference  seems  to 
justify  its  publication  here. 

Soils  may  be  variously  classified  according  to  their  geological 
formation,  the  nature  of  the  parent  rocks  from  which  they  are  formed, 
the  degree  of  coarseness  or  fineness  of  their  physical  make-up,  their 


25  San  Joaquin  soil  is  very  similar  to  Placentia.     It  is  an  old  alluvial,  derived 
from  granitic  rocks  and  underlaid  by  hardpan  at  from  three  to  four  feet. 


Bulletin  345]  FERTILIZER  EXPERIMENTS  WITH  CITRUS  TREES  509 

chemical  composition,  their  native  flora,  or  their  agricultural  history 
and  performance.  To  what  extent  each  of  these  classifications  may 
be  of  value  to  an  orchardist  is  a  matter  of  dispute:  certainly  any 
classification,  to  be  of  value,  needs  to  be  carefully  interpreted. 

Citrus  fruits  are  grown  on  a  wide  range  of  soils  in  southern  Cali- 
fornia, and  yet  these  soils  generally  fall  into  a  comparatively  few  gen- 
eral groups.  If  the  classification  of  the  Bureau  of  Soils  is  used,  it  is 
found  that  not  less  than  90  per  cent  of  citrus  planting  in  southern 
California26  is  on  soils  belonging  to  the  Hanford,  Yolo,  Ramona  or 
Placentia  series.    The  preponderance  is  in  the  order  given. 

Hanford  soils  are  recent  alluvials,  derived  from  granitic  rocks, 
light  brown  in  color,  moderate  to  low  in  organic  matter,  high  in  alkali- 
forming  bases  (potassium  and  sodium),  never  underlain  by  hardpan 
but  often  by  coarse  gravel.  The  native  vegetation  is  various,  but  is 
predominatingly  composed  of  good  to  heavy  cover  of  coarse  chaparral 
with  sparse  foliage.27  This  growth  is  mainly  perennial,  with  short 
and  sparse  grass  and  other  annual  development.  Occasional  oak 
groves  are  noted,  and  sycamores  follow  the  stream  courses.  Alfilaria 
and  occasionally  malva  are  sometimes  rank  on  newly  cleared  tracts. 

Yolo  soils  are  also  of  recent  alluvial  origin,  but  are  derived  from 
shales  and  other  sedimentary  rocks.  They  are  gray  or  light  brown  in 
color,  moderately  to  well  supplied  with  organic  matter,  moderate  to 
low  in  potassium  and  sodium,  never  underlain  by  hardpan  but  fre- 
quently by  a  heavier  loam  than  the  surface,  and  occasionally  the  sub- 
soil is  very  high  in  lime.  Drainage  is  apt  to  be  poorer  than  in  the 
Hanford  series  and  therefore  alkali  accumulations  are  commonly 
injurious  in  the  lowlying  tracts.  The  native  vegetation  is  predom- 
inatingly composed  of  rank-growing  annuals  of  which  the  mustards 
and  malvas  possibly  are  most  general.  Tree  growth  is  largely  limited 
to  willows,  in  the  moist  locations. 

Ramona  soils,  derived  from  granitic  rocks,  are  of  much  older 
alluvial  origin.  They  are  light  brown  to  light  red  in  color,  low  in 
organic  matter,  high  in  potassium  and  sodium,  sometimes  underlain 


26  Tulare  County  presents  a  rather  different  range  of  soil  types  that  are  used 
for  citrus  planting,  including  two  series  derived  from  basic  igneous  rocks  and  two 
series  of  old  alluvial  soils  derived  largely  from  granitic  rocks. 

27  This  use  of  the  term  ' '  chaparral ' '  is  possibly  open  to  criticism.  As  used 
it  is  intended  to  include  a  number  of  woody  stemmed  perennials  of  which  the 
following  list  is  representative:  (1)  Adenostoma  fasciculatum  H.  &  A.  (grease- 
wood  or  chamiso) ;  (2)  Artemesia  califomica  Less.  (California  sage) ;  (3)  Ceno- 
thus  divaricatus  Nutt.  (California  lilac) ;  (4)  Eriogonum  fasciculatum  Beuth. 
(wild  buckwheat);  (5)  Lotus  glabra  Greene  (deer  clover);  (6)  Querents  dumosa 
Nutt.  (scrub  oak) ;  (7)  Salvia  apiana  Jepson  (white  sage) ;  (8)  Rhamnus  cali- 
fomica Esch.  (wild  coffee) ;  (9)  Bhus  laurina  Nutt.  (sumac) ;  (10)  Prunus  Uici- 
folia  Walp.  (wild  cherry). 


DIVISION  OF  SUaiROPICAL  H0RUCUL11M 

COLLEGE  OF  AGRICULTURE 

BERKELEY,  CALIFORNIA 


510  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

by  a  hardpan  at  3  to  6  feet.  Drainage  is  generally  fair  to  good.  The 
native  chaparral  is  neither  so  thick  nor  so  rank  as  on  the  Hanford 
soils,  but  is  of  much  the  same  general  character. 

Placentia  soils  are  similar  to  Ramona,  but  are  redder  in  color  and 
poorer  in  organic  material.  Hardpan  is  more  general  and  closer  to 
the  surface,  and  when  there  is  no  hardpan  there  is  frequently  a  very 
compact  clay  subsoil.  Drainage  is  apt  to  be  poor  in  spots  because  of 
the  undulating  nature  of  the  hardpan  and  the  clay  subsoil.  Native 
vegetation  is  very  sparse.  Native  tree  growth  is  almost  wholly  lack- 
ing on  both  Ramona  and  Placentia  soils. 

Generally  speaking,  all  of  these  soils  are  potentially  alkaline  and 
are  moderately  to  well  supplied  with  mineral  plant  food  elements. 

In  southern  California  there  is  almost  no  citrus  planted  on  residual 
soils.  Contributing  reasons  for  this  may  be  that  most  of  the  residual 
soils  in  the  district  are  on  rather  steep  hillsides,  where  irrigation  is 
difficult.  It  is  also  true  that  a  high  percentage  of  local  residual  soils 
are  of  heavy  texture  and  that  they  are  usually  underlain  with  bed 
rock  at  rather  shallow  depths. 

In  physical  composition  the  range  of  citrus  soils  includes  all  the 
grades  of  loams  from  gravelly  sandy  loams  to  clay  loams.  The  clay 
loams  are  limited  in  extent  and  are  rarely  used  for  citrus  except  in 
the  Whittier  area.  Silt  loams  are  common  in  the  Whittier,  Orange 
County,  and  Ventura  County  districts.  In  general,  the  lighter,  coarser 
loams  are  much  more  widely  used  for  citrus  than  the  finer  ones. 

In  the  Hanford  series  the  coarser  loams  predominate.  The  Ramona 
and  Placentia  soils  are  most  apt  to  be  medium  loams,  frequently 
underlain  with  clay  loam  subsoils,  while  the  Yolo  soils  are  more  often 
of  the  finer  texture. 

The  Hanford  soils  (loam  to  gravelly  loam)  are  found  throughout 
the  foothill  district  from  Pasadena  to  Highland  and  extend  outward 
to  include  practically  all  the  citrus  plantings  in  the  Pomona  and  east- 
ern San  Gabriel  valleys.  Much  of  the  San  Fernando  Valley,  particu- 
larly the  Mission  tract,  is  typical  of  Hanford,  as  is  also  the  land 
contiguous  to  the  Santa  Ana  River,  from  Redlands  through  to  Olive, 
Anaheim,  and  Garden  Grove. 

The  Yolo  soils  (loam,  silt  loam,  and  fine  sandy  loam)  occupy  all 
the  principal  citrus  areas  of  Ventura  County  except  the  Ojai  Valley  ;28 
the  Corona  and  the  Placentia-Fullerton  districts  and  much  of  the 
Santa  Ana-Orange-Tustin  district  are  composed  of  Yolo  soils. 

28  The  citrus  orchards  of  the  Ojai  are  planted  on  an  old  alluvial  soil  derived 
from  shales  which  have  been  classified  under  the  Ojai  series. 


BULLETIN   345]  FERTILIZER  EXPERIMENTS  WITH   CITRUS  TREES  511 

In  southern  California  the  Ramona  soils  are  found  generally  in 
smaller  blocks  than  the  Hanford  and  Yolo  series.  The  main  distri- 
bution includes  areas  south  and  east  of  Los  Angeles,  the  Alhambra 
district,  small  areas  near  Santa  Ana,  a  long  narrow  strip  at  San 
Dimas,  a  very  small  area  northwest  of  San  Fernando,  and  a  consider- 
able acreage  in  the  Riverside  region. 

The  Placentia  soils  are  almost  entirely  confined  to  the  Arlington- 
Riverside  district  and  the  Redlands  district. 

In  general  the  climate  is  cooler  and  the  rainfall  greater  in  the 
districts  where  the  Yolo  soils  predominate  than  in  those  localities 
where  the  Hanford  and  Ramona  and  Placentia  soils  are  more  common. 
As  exceptions,  Hanford  soils  are  found  in  the  strictly  coast  area  below 
Anaheim,  while  Yolo  soils  are  found  at  Corona  and  at  the  upper 
end  of  the  Little  Santa  Clara  Valley  where  the  hot  interior  climate 
prevails.  As  a  consequence  of  these  climatic  differences,  rather  than 
of  the  soil  differences,  the  Yolo  soils  are  more  generally  used  for  Valen- 
cias  and  lemons,  while  the  finest  Navel  groves  are  planted  on  Hanford 
or  occasionally  on  Ramona  soils. 


CONCLUSIONS 

Certain  points  of  emphasis  are  consistently  shown  by  each  of 
these  experiments: 

1.  There  is  a  positive  value  to  be  derived  from  fertilizing  citrus 
trees  on  any  of  the  soils  involved  in  these  trials,  as  measured  by  in- 
creased crop  yields. 

2.  This  value  seems  to  be  associated  primarily  with  the  use  of 
nitrogen. 

3.  No  definite  value  can  be  attached  to  the  use  of  potash  or  phos- 
phoric acid  in  any  of  the  trials  reported,  either  when  used  in  conjunc- 
tion with  nitrogen  or  when  used  alone. 

4.  Lime,  applied  as  ground  limestone,  has  not  been  of  value  in  the 
trials  reported  except  at  Chula  Vista  on  the  Kimball  sandy  loam  soil. 

5.  Bulky  organic  material  has  been  of  large  importance  in  citrus 
fertilization. 

6.  Specific  fertilizing  materials  have  given  different  results  in 
different  locations ;  so  much  so  that  findings  from  one  set  of  field  trials 
should  not  be  too  literally  interpreted  for  any  other  set  of  conditions. 


512  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

7.  Field  trials  with  fruit  trees  are  generally  designed  to  measure 
the  effect  of  contrasting  systems  of  orchard  management  and  cannot 
furnish  exact  answers  to  specific  questions  concerning  the  economy  of 
any  certain  kind,  amount,  or  method  of  application  of  fertilizer. 

8.  The  field  trials  and  orchard  surveys  reported  upon  in  this  pub- 
lication indicate  clearly  that  fertilization  is  required  for  the  economical 
production  of  citrus  fruits  under  usual  southern  California  conditions. 
That  the  application  of  fertilizer  is  often  delayed  too  long  after  the 
planting  of  an  orchard,  and  that  larger  applications  might  be  used 
with  profit,  are  points  that  are  also  indicated. 

9.  Groves  that  have  been  allowed  to  deteriorate  through  lack  of 
fertilizer  may  be  greatly  improved  by  the  use  of  nitrogenous  fertilizer 
materials.  Where  deterioration  is  manifested  by  typical  mottle  leaf 
and  attendant  characteristics,  it  appears  that  a  correction  of  this  par- 
ticular trouble  is  not  to  be  found  in  the  use  of  commercial  fertilizers, 
particularly  inorganic  fertilizers. 

10.  Covering  the  ground  with  a  straw  mulch,  thus  eliminating  the 
necessity  for  any  tillage  operations,  may  be  expected  greatly  to  im- 
prove run-down  citrus  groves.  This  method  of  culture  is  likely  to  be 
limited  in  effectiveness  to  a  period  of  two  or  three  years,  following 
which  ordinary  tillage  should  again  be  resorted  to.  This  system  of 
management  is  not  well  adapted  to  clay  loam  soils. 

11.  The  use  of  winter  green-manure  crops  has  been  followed  by 
conflicting  results  in  the  different  trials.  In  one  case  a  marked 
increase  in  yield  and  an  improvement  in  tree  condition  resulted;  in 
a  second  case  there  was  a  slight  decrease  in  yield ;  in  a  third  case  the 
results  seemed  to  be  negative.  The  failure  of  the  cover  crop  to  always 
produce  increased  yields  can  apparently  be  accounted  for  in  some 
cases,  but  has  not  been  in  other  cases. 


STATION  PUBLICATIONS  AVAILABLE  FOB  FBEE  DISTBIBUTION 

BULLETINS 


No.  No. 

251.  Utilization  of  the  Nitrogen  and  Organic  309. 
Matter   in    Septic   and   Imhoff   Tank 

Sludges.  310. 

253.  Irrigation  and  Soil  Conditions  in  the  312. 

Sierra  Nevada  Foothills,  California.  313. 

261.  Melaxuma    of    the    Walnut,    "Juglans  316. 

regia."  317. 

262.  Citrus  Diseases  of  Florida  and  Cuba 

Compared  with  Those  of  California.  320. 

263.  Size  Grades  for  Ripe  Olives.  321. 

267.  Experiments  with  Stocks  for  Citrus.  323. 

268.  Growing  and  Grafting  Olive  Seedlings. 

270.  A  Comparison  of  Annual  Cropping,  Bi-  324. 
ennial  Cropping,  and  Green  Manures 

on  the  Yield  of  Wheat.  325. 

273.  Preliminary  Report  on  Kearney  Vine- 
yard Experimental  Drain. 

275.  The  Cultivation  of  Belladonna  in  Cali-  330. 

fornia.  331. 

276.  The  Pomegranate.  332. 

278.  Grain  Sorghums.  334. 

279.  Irrigation  of  Rice  in  California. 

280.  Irrigation  of  Alfalfa  in  the  Sacramento  335. 

Valley. 

282.  Trials  with  California  Silage  Crops  for  336. 

Dairy  Cows. 

283.  The  Olive  Insects  of  California.  337. 

285.  The  Milk  Goat  in  California.  339. 

286.  Commercial  Fertilizers. 

287.  Vinegar  from  Waste  Fruits.  340. 
294.  Bean  Culture  in  California. 

297.  The  Almond  in  California.  341. 

298.  Seedless  Raisin  Grapes.  342. 

299.  The  Use  of  Lumber  on  California  Farms.  343. 
304.  A  Study  on  the  Effects  of  Freezes  on  344. 

Citrus  in  California. 
308.  I.  Fumigation  with  Liquid  Hydrocyanic  347. 
Acid.  II.  Physical  and  Chemical  Prop- 
erties of  Liquid  Hydrocyanic  Acid.  348. 


I.  The  Carob  in  California.  II.  Nutri- 
tive Value  of  the  Carob  Bean. 

Plum  Pollination. 

Mariout  Barley. 

Pruning  Young  Deciduous  Fruit  Trees. 

The  Kaki  or  Oriental  Persimmon. 

Selections  of  Stocks  in  Citrus  Propa- 
gation. 

Control  of  the  Coyote  in  California. 

Commercial  Production  of  Grape  Syrup. 

Heavy  vs.  Light  Grain  Feeding  for 
Dairy  Cows. 

Storage  of  Perishable  Fruit  at  Freezing 
Temperatures. 

Rice  Irrigation  Measurements  and  Ex- 
periments in  Sacramento  Valley, 
1914-1919. 

Dehydration  of  Fruits. 

Phylloxera-Resistant  Stocks. 

Walnut  Culture  in  California. 

Preliminary  Volume  Tables  for  Second- 
Growth  Redwoods. 

Cocoanut  Meal  as  a  Feed  for  Dairy 
Cows  and  Other  Livestock. 

The  Preparation  of  Nicotine  Dust  as 
an  Insecticide. 

Some  Factors  of  Dehydrater  Efficiency. 

The  Relative  Cost  of  Making  Logs  from 
Small  and  Large  Timber. 

Control  of  the  Pocket  Gopher  in  Cali- 
fornia. 

Studies  on  Irrigation  of  Citrus  Groves. 

Hog  Feeding  Experiments. 

Cheese  Pests  and  Their  Control. 

Cold  Storage  as  an  Aid  to  the  Market- 
ing of  Plums. 

The  Control  of  Red  Spiders  in  Decidu- 
ous Orchards. 

Pruning  Young  Olive  Trees. 


CIRCULARS 


No.  No. 
70.   Observations    on    the    Status    of   Corn  172. 
Growing  in  California.  173. 
82.  The  Common  Ground  Squirrels  of  Cali- 
fornia. 174. 
87.  Alfalfa.  175. 

110.  Green  Manuring  in  California. 

111.  The  Use  of  Lime  and  Gypsum  on  Cali-  178. 

fornia  Soils.  179. 
113.  Correspondence  Courses  in  Agriculture. 

115.   Grafting  Vinifera  Vineyards.  181. 

126.  Spraying  for  the  Grape  Leaf  Hopper. 

127.  House  Fumigation.  182. 
129.  The  Control  of  Citrus  Insects. 

138.  The  Silo  in  California  Agriculture.  183. 

144.  Oidium  or  Powdery  Mildew  of  the  Vine.  184. 

148.   "Lungworms."  188. 

151.  Feeding  and  Management  of  Hogs.  189. 

152.  Some  Observations  on  the  Bulk  Hand-  190. 

ling  of  Grain  in  California.  193. 

155.  Bovine  Tuberculosis.  198. 

157.  Control  of  the  Pear  Scab.  201. 

159.  Agriculture  in  the  Imperial  Valley.  202. 
161.  Potatoes  in  California. 

164.  Small  Fruit  Culture  in  California.  203. 

165.  Fundamentals  of   Sugar  Beet  Culture  205. 

under  California  Conditions.  206. 

166.  The  County  Farm  Bureau.  208. 

167.  Feeding  Stuffs  of  Minor  Importance. 

169.  The  1918  Grain  Crop.  209. 

170.  Fertilizing  California  Soils  for  the  1918  210. 

Crop.  212. 


Wheat  Culture. 

The   Construction   of   the   Wood-Hoop 

Silo. 
Farm  Drainage  Methods. 
Progress  Report  on  the  Marketing  and 

Distribution  of  Milk. 
The  Packing  of  Apples  in  California. 
Factors   of   Importance   in   Producing 

Milk  of  Low  Bacterial  Count. 
Control     of     the     California     Ground 

Squirrel. 
Extending  the  Area  of  Irrigated  Wheat 

in  California  for  1918. 
Infectious  Abortion  in  Cows. 
A  Flock  of  Sheep  on  the  Farm. 
Lambing  Sheds. 
Winter  Forage  Crops. 
Agriculture  Clubs  in  California. 
A  Study  of  Farm  Labor  in  California. 
Syrup  from  Sweet  Sorghum. 
Helpful  Hints  to  Hog  Raisers. 
County  Organizations  for  Rural  Fire 

Control. 
Peat  as  a  Manure  Substitute. 
Blackleg. 
Jack  Cheese. 
Summary  of  the  Annual  Reports  of  the 

Farm  Advisors  of  California. 
The  Function  of  the  Farm  Bureau. 
Suggestions  to  the  Settler  in  California. 
Salvaging  Rain-Damaged  Prunes. 


CIRCULARS — Continued 


No.  No. 

214.  Q— d  Treatment  for  the  Prevention  of  236. 

eal  Smuts. 

215.  I\c^ing  Dairy  Cows  in  California. 

217.  Methods  for  Marketing   Vegetables  in  237. 

California. 

218.  Advanced    Registry   Testing   of   Dairy  238. 

Cows.  239. 

219.  The  Present  Status  of  Alkali. 

223.  The  Pear  Thrips.  240. 

224.  Control   of  the    Brown   Apricot    Scale 

and  the  Italian  Pear  Scale  on  Decid-  241. 

uous  Fruit  Trees. 

225.  Propagation  of  Vines.  242. 

227.  Plant  Diseases  and  Pest  Control.  243. 

228.  Vineyard  Irrigation  in  Arid  Climates. 

230.  Testing  Milk,   Cream,   and   Skim  Milk  244. 

for  Butterfat.  245. 

231.  The  Home  Vineyard.  246. 
282.  Harvesting    and    Handling    California 

Cherries  for  Eastern  Shipment.  247. 

233.  Artificial  Incubation.  248. 

234.  Winter  Injury  to  Young  Walnut  Trees 

during  1921-22.  249. 

235.  Soil  Analysis  and  Soil  and  Plant  Inter-  252. 

relations.  .  253. 


The  Common  Hawks  and  Owls  of  Cali- 
fornia from  the  Standpoint  of  the 
Rancher. 

Directions  for  the  Tanning  and  Dress- 
ing of  Furs. 

The  Apricot  in  California. 

Harvesting  and  Handling  Apricots  and 
Plums  for  Eastern  Shipment. 

Harvesting  and  Handling  Pears  for 
Eastern  Shipment. 

Harvesting  and  Handling  Peaches  for 
Eastern  Shipment. 

Poultry  Feeding. 

Marmalade  Juice  and  Jelly  Juice  from 
Citrus  Fruits. 

Central  Wire  Bracing  for  Fruit  Trees. 

Vine  Pruning  Systems. 

Desirable  Qualities  of  California  Bar- 
ley for  Export. 

Colonization  and  Rural  Development. 

Some  Common  Errors  in  Vine  Pruning 
and  Their  Remedies. 

Replacing  Missing  Vines. 

Supports,  for  Vines. 

Vineyard  Plans. 


NIVKRSJTY  of  CALIFORNIA 

LOS  ANGELK3 
LIBRARY 


DMSKM  Of  Su*.KOPir.AL  HORTICULTURE 

COLLEGE  OF  AGRICULTURE 

BERKELEY.  CALIFORNIA' 


fMs  book  is  DI1^  on  the  last  date  stamof 


SB 
V19f 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


A    001  095  398    2 


